Setting field-mapping properties  Configuring table-mapping properties

Chapter 27: Creating Entity Components

Specifying finder- and ejbSelect-method queries

Each finder method in the component’s home interface requires a database query to select a set of primary keys. For example, the findByPrimaryKey method selects the key that matches the input parameter. A findAll method might return all keys in the table. ejbSelect methods in an EJB 2.0 entity bean also require query mappings.

There are two ways to specify query mappings:

NoteIf you have deployed EJB CMP entity beans from an EJB-JAR file If you have deployed EJB CMP entity beans from an EJB-JAR file, the special query mapping value [unknown] indicates that you must specify a query. The special value [default] means that EAServer can infer the query based on the method’s name pattern. The special value ejbQuery: indicates the query uses EJB-QL that was specified in the deployment descriptor.

StepsConfiguring queries for methods

  1. Display the Persistence/Query Mapping subtab in the Component Properties dialog box. One mapping displays for each finder method in the component’s home interface and for each ejbSelect method.

  2. To change the query mapping, highlight the method name or query, then click Modify. Edit the value as follows:

    Using EJB-QL: The special EAServer query ejbQuery: indicates that an EJB-QL query is defined for the finder or ejbSelect method. You can add additional parameters to configure caching of the query results, as described in “Entity instance and query caching” in the EAServer Performance and Tuning Guide, for example:

    ejbQuery:[cache]
    

    If the special mapping ejbQuery: is specified for the method, the EJB-QL query can be specified using a second query mapping for the method. The EJB-QL query must follow the syntax described by the EJB 2.0 specification.

    In EJB-QL, each entity bean is represented by a schema name. EAServer defines the EJB-QL schema names in the properties of the package that contains the component. To map schema names to components in the package, specify a package property of the form:

    schema:name=package/component
    

    Where name is the schema name, package is the EAServer package name and component is the component name. If the package properties do not specify a schema name for the component, the default is the component name. Schemas used in queries for a component can only refer to components in the same EAServer package.

    Using EAServer extended SQL: Enter one of the following for the query:

    Noteselect queries for ejbSelect methods can return one column only.

Extended SQL examples

Use the syntax of these examples if you are using database tables that can be accessed directly with standard SQL select statements.

For simple queries that select only from the main table, you can omit the select keyword and column list as in this example. This query uses the value of the expiryDate parameter to filter a range of closingDate column values. Note the select keyword, column list, and from clause are omitted:

where closingDate < @expiryDate

When you omit the select keyword for a finder query, all columns are selected. If you are using query caching, selecting all columns allows EAServer to preload the query cache when the finder method executes.

If you include the select keyword and a column list in the query, you must use binding syntax (pseudoassignments) to bind the selected columns to the container-managed fields unless you are using the [key] placeholder for the table’s primary key, as in:

select @field1 = col1, @field2 = (select col2 from t2 where t2.a = t1.a) from table1 t1, table2 t2

In this example, field1 and field2 are the names of the container-managed fields that are bound to the columns returned in the result set.

If you specify a column list and you are using entity object caching, specify a select list that returns all columns so that the object cache can be populated from the query results. Omit the select keyword, the column list, and the from clause to avoid this complication.

The query must be a complete select statement or omit the select keyword, column list, and from clause.

Calling stored procedures in extended SQL

You can call stored procedures to return the results required to execute a finder or ejbSelect query. To specify a stored procedure call, use the syntax:

select column-list from {call proc param-list}

Where:

For example, you might use this query for a findByPrimaryKey method:

select @firstName, @lastName, @ts from {call sp_select_CustomerProcs @primaryKey}




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