Vaadin SLQContainer 0.8 User Manual Table of Contents
Contents
1. Note that a call to the refresh method will not affect or reset the following properties of the container The QueryDelegate of the container e Autocommit mode e Page length e Filters Sorting 4 3 4 Cache flush notification mechanism Cache usage with databases in multiuser applications always results in some kind of a compromise between the amount of queries we want to execute on the database and the amount of memory we Vaadin SQLContainer 0 8 User Manual want to use on caching the data and most importantly risking the cached data becoming stale SQLContainer provides an experimental remedy to this problem by implementing a simple cache flush notification mechanism Due to its nature these notifications are disabled by default but can be easily enabled for a container instance by calling enableCacheFlushNotifications at any time during the lifetime of the container The notification mechanism functions by storing a weak reference to all registered containers in a static list structure To minimize the risk of memory leaks and to avoid unlimited growing of the reference list dead weak references are collected to a reference queue and removed from the list every time a SQLContainer is added to the notification reference list or a container calls the notification method When a SQLContainer has its cache notifications set enabled it will call the static notifyOfCacheFlush method giving itself as a parameter This met2. Object propertylId public void removeAllContainerFilters These methods will remove filters added with either addFilter or addContainerFilter method 4 1 2 Filtering mode Currentle the SQLContainer has limited support for two filtering modes The modes are defined in the FilteringMode enum which is located in the query package The two modes are called exclusive and inclusive Exlusive mode means that in the generated query all the filtering rules will be joined with an OR Inclusivu mode means that AND will be used The default filtering mode is inclusive AND filtering Vaadin SQLContainer 0 8 User Manual 4 1 3 Sorting Sorting can be performed either using the Vaadin provided means implemented from Container Sortable using the following method where the propertyIds again refer to column names More information on the standard filtering can be found in Book of Vaadin public void sort Object propertyId boolean ascending In addition to the standard method it is also possible to directly add an OrderBy to the container via the addOrderBy OrderBy orderBy method This enables the developer to insert sorters one by one without providing the whole array of them at once Sorting rules can be cleared by calling the sort method with null or an empty array as the first argument 4 2 Editing Editing the items Rowltems of SQLContainer can be done similarly to editing the items of any Vaadin container Col
3. the TableQuery query delegate After the connection pool is created we ll need a query delegate for the SQLContainer The simplest way to create one is by using the built in TableQuery class The TableQuery delegate provides access to a defined database table and supports reading and writing data out of the box We create the TableQuery with the following statement TableQuery tq new TableQuery tablename connectionPool If we need to enable the write support we must set a version column to the TableQuery as well The version column is an integer or timestamp typed column which will either be incremented or set to the current time on each modification of the row TableQuery assumes that the database will take care of updating the version column it just makes sure the column value is correct before updating a row The following code will set the version column tq setVersionColumn OPTLOCK 3 3 Creating the container Finally we may create the container itself This is as simple as stating SQLContainer container new SQLContainer tq After this statement the SQLContainer is connected to the table tablename and is ready to use for example as a data source for a Vaadin Table or a Vaadin Form Vaadin SQLContainer 0 8 User Manual 4 Using the SQLContainer 4 1 Filtering and Sorting Filtering and sorting the items contained in an SQLContainer is by design always performed in the database In practice this means that
4. whenever the filtering or sorting rules are modified at least some amount of database communication will take place the minimum is to fetch the updated row count using the new filtering sorting rules 4 1 1 Filtering Filtering can be performed either using the Vaadin provided means implemented from Container Filterable using the following method where propertyId means column name in the SQLContainer context More information on the standard filtering can be found in Book of Vaadin public void addContainerFilter Object propertylId String filterString boolean ignoreCase boolean onlyMatchPrefix Note Using the standard method only allows filtering on String typed properties Numeric types dates etc must be filtered using the Filter class see below In addition to the standard method it is also possible to directly add a Filter to the container via the addFilter Filter filter method This enables the developer to take advantage of a few more features including e More comparison methods via Filter ComparisonType e EQUALS GREATER LESS GREATER OR EQUAL LESS OR EQUAL STARTS WITH ENDS WITH CONTAINS e BETWEEN e Filtering of numeric and other non String types e Two valued filtering via Filter setSecondValue Object second Value e Implicit setting for need of quoting via setNeedsQuotes boolean needsQuotes Removing the filtering rules is also done via the standard Vaadin methods public void removeContainerFilters
5. N 12 5 3 Creating your own FreeformStatementDelegate nneneeeeeseeeseeseosseeseesrossressseresssrerssseeesseee 12 6 Non implemented methods of Vaadin container interfaces cssccsscsccssssccssssccsssseesssseeees 14 6 1 About the getItemIds tne hod ack casew oxcscetnsaeccmealaceinnesiacmesiius cvienddbcoobants hateecmenrevn washes ces 14 Ts ADPCM COS P EE E AT 15 Pc SUD POLE K FTP i YTI ERES AE E AEAEE EASE E NAA E E E AEE A E E 15 B Known issues and limitations of SQLContainet cccccccesccccessccesseeeesseceesseeeesseceesseeesesseeeees 15 C Planned features nesana ia a A E E N EE ain E Aan 15 Vaadin SQLContainer 0 8 User Manual 1 Introduction Vaadin SQLContainer is a Vaadin container implementation that allows easy and customizable access to data stored in various SQL speaking databases see appendix A for details SQLContainer supports two types of database access Using TableQuery the pre made query generators will enable fetching updating and inserting data directly from the container into a database table automatically whereas FreeformQuery allows the developer to use their own probably more complex query for fetching data and their own optional implementations for writing filtering and sorting support item and property handling as well as lazy loading will still be handled automatically In addition to the customizable database connection options SQLContainer also extends the Vaad
6. Vaadin SLQContainer 0 8 User Manual Teppo Kurki 2010 Vaadin Ltd Table of Contents 1 TMEV O DU COON o5 setae siecccd cents cncce catenneebaeiesecascusicocas cosceuabanteseactnacdancockduteduexsnckdsoctvasadessumveneseadecd avec seseuses 2 Ze PRECIO CUI EG sooo scutes xsccteci consis vascasucscacetbaueusue lacs cetcpevcactbuccsaauancusuaue fave doushavelatadecaacsene o eses 3 3 Getting started with SQULCOmtanmen cisscsscsscdsssccsstssessinussncetssssossssdunscesstcsasnisecneassvesocanasdeseasoavesaeses 5 3 1 Creating a connection POON addi cssce tie SenucaiendardnsncCess ps nu thas Saves atte dunnctdeadedecutoes Aeecdtiad ots cusienes 5 3 2 Creating the lableQuery query dele ate icy cc d 002 eaveystectanpbanncunvsere buat ciaatiagsteettayvoneuqaemenaneace 5 3 3 Creating the containere a aby cacy E svete ames rcas EAE a A aati 5 4 Using th SOU C mba er ssiessssesascsisus ssasescnavsds sosevenspessiocdsuccuaseseraseesunssuenessvadedseesasenoscsnestassaswassaaatines 6 4l Filtering and VSO ERT sa ae lat oa ae caer ug Sede cay Ny ae elas peers ca deed ea vss cuneate 6 BV cd Filter nonin cto ai noes aaa te E A ak Te cds Fea E Ha css SMG OE alee 6 Folks Dy Filtering THO esseri aeaea aaaea goed been vey habe E E she a anual yond penis bahdens olay 6 FA DS SOL ME ROR E eRe EE ill GB Rc PE Oa ETE RO NB OR atl OIR S 4 42 EdUND aa vp ng Cat ev eects Nw co esate lees Se ov ee Maca leencano a a tiga 7 4 21 Adding t ms a erain elles E E E ulead AE A V
7. ania A a EN Da ai A AAA A ta a EE NA 7 4 2 2 Fetching generated row REVS ii dcdicecscdyescesuieateetupeageuusencaciuyncteattaitcltbeteetcvesetatash ukabecanee 7 4 2 3 Version column VEQUITEMICTL eosixsisodsciesauaustikons i loSmeryat wenn wasiauadits varie isoeeasy anealetntarethes ts amp 423 A to commit Modere 0525 os ic SOY eSB sya A AE Sega MANA Riedie Te amp 42 4 Modified state isida shea a Soa dos shaves dad abate nese aad hovel A E NE ca beeabeh ere Ei amp 4 3 Caching paging and Temes Wim gic yssi cont recccaeetsieas sch acces snbonsdbseeDbnes Said eh a a sabe Aae aaaeei 8 4 3 Vs Container SIZE eo adc ph be a lati Wit haa Nee aa ea T a A a a AE 9 4 3 2 Page length and cache sizeren unani e n A R E ERA daon s 9 4 3 3 Refreshing the container nssonennnnaeeneseesisseesesresseertsresseesrtsresstesresrtsstesresrersssreessree 9 4 3 4 Cache flush notification MECHANISM svesiossssas viexasunnyorva alk nossd cesesoatedsbouadasneeasn pisces Aaagnuliadraieee 9 4 4 Referencing another SQLContainer cccccceccccsscesseceseeeececeseceeeecneeeseecnseceeeceeeeeeeenseeenseenes 10 5 Using FreeformQuery and FreeformStatementDelegate csssccscsscscssscsscsscsscscsssscssseees 12 ks GEM OSTATICG cennar ne cxdacstaseantatgate asteaassateeevancndasasatecsletsaucadleuanin autem ta cisecesameainesuen dace 12 5 2 Limita hons 9 08 seh shaytesesanadinoyabagncowsdnd csiva suas tome a guy En cians dedi EEA a eTa dun EEES aeaa E NATE
8. ate To create your own delegate for FreeformQuery you must implement some or all of the methods from the FreeformStatementDelegate interface depending on which ones your use case requires The interface contains eight methods which are shown below For more detailed requirements see the JavaDoc documentation of the interface Read only queries public StatementHelper getCountStatement public StatementHelper getQueryStatement int offset int limit public StatementHelper getContainsRowQueryStatement Object keys Filtering and sorting public void setFilters List lt Filter gt filters public void setFilters List lt Filter gt filters FilteringMode filteringMode public void setOrderBy List lt OrderBy gt orderBys Write support 12 Vaadin SQLContainer 0 8 User Manual public int storeRow Connection conn RowItem row public boolean removeRow Connection conn RowItem row A simple demo implementation of this interface can be found in the SQLContainer package more specifically in the class com vaadin addon sqlcontainer demo DemoFreeformQueryDelegate 13 Vaadin SQLContainer 0 8 User Manual 6 Non implemented methods of Vaadin container interfaces Due to the database connection inherent to the SQLContainer some of the methods from the container interfaces of Vaadin can not or would not make sense to be implemented These methods are l
9. d by SQLContainer when necessary To receive updates on the row IDs you might use the following code assuming container is an instance of SQLContainer Note that these events are not fired if auto commit mode is enabled app getDbHelp getCityContainer addListener new QueryDelegate RowIdChangeListener public void rowIdChange RowIdChangeEvent event System err printin Old ID is event getOldRowId System err printin New ID is vent getNewRowld Vaadin SQLContainer 0 8 User Manual 4 2 3 Version column requirement If you are using the TableQuery class as the query delegate to the SQLContainer and need to enable write support there is an enforced requirement of specifying a version column name to the TableQuery instance The column name can be set to the TableQuery using the following statement tq setVersionColumn OPTLOCK The version column is preferrably an integer or timestamp typed column in the table that is attached to the TableQuery This column will be used for optimistic locking before a row modification the TableQuery will check before that the version column value is the same as it was when the data was read into the container This should ensure that no one has modified the row inbetween the current user s reads and writes Note TableQuery assumes that the database will take care of updating the version column by either using an actual VERSION column if suppor
10. ed item As parameters this method needs the item ID of the referencing item and a reference to the target container as an identifier SQLContainer also provides a convenience method getReferencedItem which directly returns the referenced item from the target container Finally the referencing can be removed from the source container by calling the removeReference method with the target container as parameter Note that this does not actually change anything in the database it merely removes the logical relation that exists only on the Java side 11 Vaadin SQLContainer 0 8 User Manual 5 Using FreeformQuery and FreeformStatementDelegate In most cases the provided TableQuery will be enough to allow a developer to gain effortless access to an SQL data source However there may arise situations when a more complex query with e g joins is needed Or perhaps you need to redefine how the writing or filtering should be done The FreeformQuery query delegate is provided for this exact purpose Out of the box the FreeformQuery supports read only access to a database but it can be extended to allow writing also 5 1 Getting started Getting started with the FreeformQuery may be done as shown in the following The connection pool initialization is similar to the TableQuery example so it is omitted here Note that the name s of the primary key column s must be provided to the FreeformQuery manually This is required because de
11. er M anual FilteringMode FILTERING MODE INCLUSIVE FILTERING MODE EXCLUSIVE lt lt interface gt gt Container ItemSetChangeNotifier N lt lt interface gt gt Container Filterable W lt lt interface gt gt 1 Container Ordered lt lt interface gt gt Container Sortable lt lt interface gt gt lt Container Indexed Container q a 3 po o fal o V V A Implemented by the user for sorting filtering and write support lt lt interface gt gt FreeformQueryDelegate setFilters filters List lt Filter gt setOrderBy orderBys List lt OrderBy gt void int storeRow row RowItem 0 1 FreeformQuery queryString String setDelegate delegate FreeFormQueryDelegate void J2EEConnectionPool column String value Object secondValue Object OrderBy comparisonType ComparisonType 1 isCaseSensitive boolean needsQuotes boolean olumn String sAscending boolean SQLContainer TemporaryRowld refresh void setAutoCommit autoCommitEnabled boolean isAutoCommit boolean setPageLength pageLength int void getPageLength void commit void rollback void addFilter filter Filter void addOrderBy orderBy OrderBy void setFilteringMode filteringMode FilteringMode void isModified boolean void lt gt lt lt interface gt gt QueryDelegate getCount int getResults offset int pagelength int Re
12. gate RowldChangeNotifier A 1 q releaseConnection conn Connection void destroy void tableName String sqlGenerator SQLGenerator SimpleJDBCConnectionPool initialConnections int maxConnections int connectionUri String userName String password String Figure 1 Detailed class diagram of SOLContainer and its supporting classes Vaadin SQLContainer 0 8 User Manual 3 Getting started with SQLContainer Gettting development going with the SQLContainer is easy and quite straight forward The purpose of this chapter is to describe how to create the required resources and how to fetch data from and write data to a database table attached to the container 3 1 Creating a connection pool First we need to create a connection pool to allow the SQLContainer to connect to a database Here we will use the SimpleJDBCConnectionPool which is a basic implementation of connection pooling with JDBC data sources In the following code we create a connection pool that uses the HSQLDB driver together with an in memory database The initial amount of connections is 2 and the maximum amount is set at 5 Note that the database driver connection url username and password parameters will vary depending on the database you are using JDBCConnectionPool connectionPool new SimpleJDBCConnectionPool org hsqldb jdbc JDBCDriver jJdbc hsqldb mem sqlcontainer SA 2 5 3 2 Creating
13. hod will compare the notifier container to all the others present in the reference list To fire a cache flush event the target container must have the same type of QueryDelegate either TableQuery or FreeformQuery and the table name or query string must match with the container that fired the notification If a match is found the refresh method of the matching container is called resulting in cache flushing in the target container Note Standard Vaadin issues apply even if the SQLContainer is refreshed on the server side the changes will not be reflected to the UI until a server round trip is performed or unless a push mechanism is used 4 4 Referencing another SQLContainer When developing a database connected application there is usually a need to retrieve data related to one table from one or more other tables In most cases this relation is achieved with a foreign key reference where a column of the first table contains a primary key or candidate key of a row in another table SQLContainer offers limited support for this kind of referencing relation although all referencing is currently done on the Java side so no constraints need to be made in the database A new reference can be created by calling the following method public void addReference SQLContainer refdCont String refingCol String refdCol This method should be called on the source container of the reference The target container should be given as the first paramete
14. in container interface to implement a bit more advanced and more database oriented filtering rules Finally the add on also offers connection pool implementations for JDBC connection pooling and JEE connection pooling as well as integrated transaction support auto commit mode is also provided The purpose of this manual is to briefly explain the architecture and some of the inner workings of SQLContainer It will also give the readers some examples on how to use SQLContainer in their own applications The requirements limitations and further development ideas are also discussed Vaadin SQLContainer 0 8 User Manual 2 Architecture The architecture of SQLContainer is relatively simple and it is described in detail in this section SQLContainer is the class implementing the Vaadin container interfaces and providing access to most of the functionality of this add on The standard Vaadin Properties and Items have been extended by the ColumnProperty and RowItem classes Item IDs are represented by RowId and TemporaryRowl1Id classes The Rowld class is built based on the primary key columns of the connected database table or query result In the connection package the JDBCConnectionPool interface defines the requirements for a connection pool implementation Two implementations of this interface are provided SimpleJDBCConnectionPool provides a simple yet very usable implementation to pool and access JDBC connections J2EEConnectionPool pr
15. is fetching a set of rows to the item cache lazy loading 4 3 2 Page length and cache size The page length of the SQLContainer dictates the amount of rows fetched from the database in one query The default value is 100 and it can be modified with the setPageLength method To avoid constant queries it is recommended to set the page length value to at least 5 times the amount of rows displayed in a Vaadin Table obviously this is also dependent on the cache ratio set for the Table component The size of the internal item cache of the SQLContainer is calculated by multiplying the page lenght with the cache ratio set for the container The cache ratio can only be set from the code and the default value for it is 2 Hence with the default page length of 100 the internal cache size becomes 200 items This should be enough even for larger Tables while ensuring that no huge amounts of memory will be used on the cache 4 3 3 Refreshing the container Normally the SQLContainer will handle refreshing automatically when required However there may be situations where an implicit refresh is needed e g to make sure that the version column is up to date prior to opening the item for editing in a form For this purpose a refresh method is provided This method simply clears all caches resets the current item fetching offset and sets the container size dirty Any item related call after this will inevitably result into row count and item cache update
16. isted below and they will throw an UnsupportedOperationException on invocation public boolean addContainerProperty Object propertylId Class lt gt type Object defaultValue public boolean removeContainerProperty Object propertylId public Item addItem Object itemId public Object addItemAt int index public Item addItemAt int index Object newItemId public Object addItemAfter Object previousItemId public Item addItemAfter Object previousItemId Object newItemId Additionally the following methods of the Item interface are not supported in the RowlItem class public boolean addItemProperty Object id Property property public boolean removelItemProperty Object id 6 1 About the getItemIds method To properly implement the Vaadin Container interface a getItemIds method has been implented in the SQLContainer By definition this method returns a collection of all the item IDs present in the container What this means in the SQLContainer case is that the container has to query the database for the primary key columns of all the rows present in the connected database table It is obvious that this could potentially lead to fetching tens or even hundreds of thousands of rows in an effort to satisfy the method caller This will effectively kill the lazy loading properties of SQLContainer and therefore the following warning is expressed here It is highly recommended not to call the get
17. itemIds method unless it is known that in the use case in question the item ID set will always be of reasonable size 14 Vaadin SQLContainer 0 8 User Manual 7 Appendices A Supported databases The following databases are supported by SQLContainer and TableQuery classes by default e HSQLDB 1 8 or newer e MySQL 5 1 or newer e PostgreSQL 8 4 or newer e Oracle Database 10g or newer e Microsoft SQL Server 2005 or newer B Known issues and limitations of SQLContainer At this point there are still some known issues and limitations affecting the use of SQLContainer in certain situations The known issues and brief explanations are listed below e Some SQL data types do not have write support when using TableQuery e All binary types e All custom types e CLOB if not converted automatically to a String by the JDBC driver in use See com vaadin addon sqlcontainer query generator StatementHelper for details e When using Oracle or MS SQL database the column name rownum can not be used as a column name in a table connected to SQLContainer e This limitation exists because the databases in question do not support limit offset clauses required for paging Instead a generated column named rownum is used to implement paging support The permanent limitations are listed below These can not or most probably will not be fixed in future versions of SQLContainer e The getItemIds method is very inefficien
18. ovides means to access J2EE DataSources The query package contains the QueryDelegat interface which defines everything the SQLContainer needs to enable reading and writing data to and from a database As discussed earlier two implementations of this interface are provided TableQuery for automatic read write support for a database table and FreeformQuery for customizing the query sorting filtering and writing this is done by implementing relevant methods of the FreeformStatementDelegate interface The query package also contains Filter and OrderBy classes which have been written to provide an alternative to the standard Vaadin container filtering and make sorting non String properties a bit more user friendly Finally the generator package contains a SQLGenerator interface which defines the kind of queries that are required by the TableQuery class The provided implementations include support for HSQLDB MySQL PostgreSQL DefaultSQLGenerator Oracle OracleGenerator and Microsoft SQL Server MSSQLGenerator A new or modified implementation may be provided to gain compatibility with older versions or other database servers A class diagram of SQLContainer and its supporting classes as well as connections to Vaadin interfaces is provided in figure 1 Note that not every method is shown in the diagram due to space constraints For further detail refer to the SQLContainer API documentation Vaadin SQLContainer 0 8 Us
19. pending on the query the result set may or may not contain data about primary key columns In this example there is one primary key column with a name ID FreeformQuery query new FreeformQuery SELECT FROM SAMPLE connectionPool ID SQLContainer container new SQLContainer query 5 2 Limitations While this looks just as easy as with the TableQuery do note that there are some important caveats here Using FreeformQuery like this without providing FreeformQueryDelegate or FreeformStatementDelegate implementation it can only be used as a read only window to the resultset of the query Additionally filtering sorting and lazy loading features will not be supported and the row count will be fetched in quite an inefficient manner Bearing these limitations in mind it becomes quite obvious that the developer is in reality meant to implement the FreeformQueryDelegate or FreeformStatementDelegate interface The FreeformStatementDelegate interface is an extension of the FreeformQueryDelegate interface which returns StatementHelper objects instead of pure query Strings This enables the developer to use prepared statetemens instead of regular statements It is highly recommended to use the FreeformStatementDelegate in all implementations From this chapter onwards we will only refer to the FreeformStatementDelegate in cases where FreeformQueryDelegate could also be applied 5 3 Creating your own FreeformStatementDeleg
20. r The refingCol is the name of the foreign key column in the source container and the refdCol is the name of the referenced key column in the target container Note For any SQLContainer all the referenced target containers must be different You can not reference the same container from the same source twice Handling the referenced item can be done through the three provided set get methods and the reference can be completely removed with the removeReference method Signatures of these methods are listed below public boolean setReferencediItem Object itemId Object refdItemId SQLContainer refdCont public Object getReferencedItemId Object itemId SQLContainer refdCont public Item getReferencedItem Object itemId SQLContainer refdCont public boolean removeReference SQLContainer refdCont The setter method should be given three parameters itemId is the ID of the referencing item from the source container refdItemId is the referenced itemID from the target container and 10 Vaadin SQLContainer 0 8 User Manual refdCont is a reference to the target container that identifies the reference This method returns true if the setting of the referenced item was successful After setting the referenced item you must normally call commit on the source container to persist the changes to the database The getReferencedItemId method will return the item ID of the referenc
21. sultSet setFilters filters List lt Filter gt void setOrderBy orderBys List lt OrderBy gt void storeRow row RowItem int beginTransaction void void void getPrimaryKeyColumns List lt String gt implementationRespectsPagingLimits boolean setFilters filters List lt Filter gt filteringMode FilteringMode void removeRow row RowItem boolean containsRowWithKey keys Object boolean void Rowa lt lt interface gt gt Property i Item A ColumnProperty allowReai y owner RowItem V __ Rowltem gt lt gt getId RowId getContainer SQLContainer isModified boolean BF OracleGenerator MSSQLGenerator gt DefaultSQLGenerator kx lt lt interface gt gt SQLGenerator generateSelectQuery tableName String filters List lt Filter gt orderBys List lt OrderBy gt offset int pageLength int toSelect String String generateSelectQuery tableName String filters List lt Filter gt filterMode FilteringMode orderBys List lt OrderBy gt offset int pagelength int toSelect int String generateUpdateQuery tableName String item RowItem String generateInsertQuery tableName String item RowItem String generateDeleteQuery tableName String item RowItem String lt lt interface gt gt r QueryDelegate RowldChangeEvent lt lt interface gt gt QueryDelegate RowldChangeListener lt lt interface gt gt QueryDele
22. t avoid calling it unless absolutely required e When using FreeformQuery without providing a FreeformStatementDelegate the row count query is very inefficient avoid using FreeformQuery without implementing at least the count query properly e When using FreeformQuery without providing a FreeformStatementDelegate writing sorting and filtering will not be supported e When using Oracle database most or all of the numeric types are converted to jJava math BigDecimal by the Oracle JDBC Driver e This is a feature of how Oracle DB and the Oracle JDBC Driver handles data types C Planned features e Provide support for all or most SQL data types e Provide means for the developer to specify their own database type to Java type mapping 15
23. ted by the database in question or by a trigger or a similar mechanism If you are certain that you do not need optimistic locking but do want to enable write support you may point the version column to e g a primary key column of the table 4 2 3 Autocommit mode SQLContainer is by default in transaction mode which means that actions that edit add or remove items are recorded internally by the container These actions can be either committed to the database by calling commit or discarded by calling rollback The container can also be set to auto commit mode When this mode is enabled all changes will be committed to the database immediately To enable or disable the auto commit mode call the following method public void setAutoCommit boolean autoCommitEnabled It is recommended to leave the auto commit mode disabled since it ensures that the changes can be rolled back if any problems are noticed within the container items Using the auto commit mode will also lead to failure in item addition if the database table contains non nullable columns 4 2 4 Modified state When used in the transaction mode it may be useful to determine whether the contents of the SQLContainer have been modified or not For this purpose the container provides an isModified method which will tell the state of the container to the developer This method will return true if any items have been added to or removed from the container as well as if an
24. umnProperties of a RowlItem will automatically notify SQLContainer to make sure that changes to the items are recorded and will be applied to the database immediately or on commit depending on the state of the autocommit mode 4 2 1 Adding items Adding items to the SQLContainer can only be done via the addItem method This method will create a new Item based on the connected database table column properties The new item will either be buffered by the container or commited to the database through the querydelegate depending on whether the auto commit mode see 4 2 3 has been enabled When an item is added to the container it is impossible to precisely know what the primary keys of the row will be or will the row insertion succeed at all This is why the SQLContainer will assign an instance of TemporaryRowId as a Rowld for the new item See 4 2 2 on how to fetch the actual key after the row insertion has succeeded If auto commit mode is enabled in the SQLContainer the addItem methot will return the final Rowld of the new item 4 2 2 Fetching generated row keys Since it is a common need to fetch the generated key of a row right after insertion a listener notifier has been added into the QueryDelegate interface Currently only the TableQuery class implements the RowldChangeNotifier interface and thus can notify interested objects of changed row IDs The events fill be fired after TableQuery commit has finished this method is calle
25. y value of an existing item has been modified Additionally each RowItem and each ColumnProperty have isModified methods to allow for a more detailed view over the modification status Do note that the modification statuses of RowItems and ColumnProperties only depend on whether or not the actual Property values have been modified That is they do not reflect situations where the whole Rowltem has been marked for removal or has just been added to the container 4 3 Caching paging and refreshing To decrease the amount of queries made to the database SQLContainer uses internal caching for database contents The caching is implemented with a size limited LinkedHashMap containing a mapping from Rowlds to Rowltems Typically developers do not need to modify caching options Vaadin SQLContainer 0 8 User Manual although some fine tuning can be done if required 4 3 1 Container size The SQLContainer keeps continuously checking the amount of rows in the connected database table in order to detect external addition or removal of rows By default the table row count is assumed to remain valid for 10 seconds This value can be altered from code class SQLContainer field sizeValidMilliSeconds If the size validity time has expired the row count will be automatically updated on e Acall to getItemIds method e Acalltosize method e Some calls to indexOfId Object itemId method e Acallto firstItemId method e When the container
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