Toplink update query

Such a query can then be repeatedly executed by name. An instance of Call that you create and then either execute directly, using a special Session API to perform limited data source actions on data only, or execute indirectly in the context of a DatabaseQuery. An instance of MethodBasedQueryRedirector taking the name of a static method and the Class in which it is defined as parameters set on a named query. When the query is executed, the static method is invoked.

Any query executed in the context of a historical session using the time-aware features of the TopLink Expression framework. The DescriptorQueryManager defines a default DatabaseQuery for each basic data source operation create, read, update, and delete , and provides an API with which you can customize either the DatabaseQuery or its Call. A query defined on the home interface of an enterprise bean that returns enterprise beans. In general, querying a data source means performing an action on or interacting with the contents of the data source.

To do this, you must be able to perform the following:. Specific to TopLink, you must also consider how the query affects the TopLink cache. For more information, see Section In TopLink, the Call object encapsulates an operation or action on a data source.

A DatabaseQuery object is an abstraction that associates additional customization and optimization options with the action encapsulated by a Call.

By separating these options from the Call , TopLink can provide sophisticated query capabilities across all Call types. Object-level queries see Section They are the preferred type of query for mapped data.

By far, object-level DatabaseQuery queries are the most common query used in TopLink. Data-level queries see Section While data-level queries return raw data and object-level queries return objects in your domain model, summary queries return data about objects.

TopLink provides partial object queries see Section In addition to storing named queries applicable to a particular class see Section TopLink expressions let you specify query search criteria based on your domain object model. When you execute the query, TopLink translates these search criteria into the appropriate query language for your platform. The Expression class represents an expression that can be anything from a simple constant to a complex clause with boolean logic.

You can manipulate, group, and integrate expressions. You can specify a selection criterion as an Expression with DatabaseQuery method setSelectionCriteria see Section A query key is a schema-independent alias for a database field name. Using a query key, you can refer to a field using a schema-independent alias. In relational projects only, TopLink automatically creates query keys for all mapped attributes. The name of the query key is the name of the class attribute specified in your object model.

You can configure query keys in a class descriptor see Section You can use query keys in expressions see Section Using TopLink, you can express a query using any of the following query languages:. In most cases, you can compose a query directly in a given query language or, preferably, you can construct a DatabaseQuery with an appropriate Call and specify selection criteria using a TopLink Expression.

Although composing a query directly in SQL appears to be the simplest approach and for simple operations or operations on unmapped data, it is , using the DatabaseQuery approach offers the compelling advantage of confining your query to your domain object model and avoiding dependence on data source schema implementation details.

SQL is the most common query language for applications that use a relational database data source. Like SQL, EJB QL is a query language; but unlike SQL, it presents queries from an object model perspective, allowing you to declare queries using the attributes of each abstract entity bean in your object model.

It also includes path expressions that enable navigation over the relationships defined between entity beans and dependent objects. You can construct queries using the attributes of the entity beans instead of using database tables and fields. The disadvantage of EJB QL queries is that it is difficult to use when you construct complex queries. Query-by-example is a simple and intuitive way to express a query. To specify a query-by-example, provide a sample instance of the persistent object to query, and set appropriate values on only the data members on which you wish to query.

Query-by-example lets you query for an object based on any attribute that uses a direct mapping or a one-to-one relationship including those with nesting.

Set only the attributes on which you base the query; set all other attributes to null. Query-by-example uses the AND operator to tie the attribute comparisons together. By default, attribute values in the sample instance are compared against corresponding values of candidate objects using EQUALS operator. You can modify this behaviour using the QueryByExamplePolicy. For more information and examples, see Section Some queries are implicitly constructed for you based on passed in arguments and executed in one step for example, session queries, as described in Section Table Session Methods for Executing a Query.

Disadvantages: less control over query execution and results; less efficient for frequently executed queries. Advantages: greatest configuration and execution flexibility; can take advantage of named queries for efficiency. Disadvantages: you must explicitly create and configure DatabaseQuery and possibly Call objects.

Disadvantages: least control over query execution and results; your application must do more work to handle raw data results. Alternatively, you can execute queries outside of a unit of work using a session API directly, but doing so places greater responsibility on your application to manage transactions, concurrency, and referential constraints.

TopLink executes DescriptorQueryManager queries when you execute a session query. You execute EJB 2. TopLink queries generally return Java objects as their result set. TopLink queries can return any of the following:.

Collections of objects see Section Partial objects, with only the attributes you specify populated and without the object reflected in the cache see Section Streams of objects see Section EJB see Section A collection is a group of Java objects contained by an instance of Collection or Map.

By default, queries that return more than one object return their results in a Vector. You can configure TopLink to return query results in any concrete instance of Collection or Map. For information and examples on how to configure and handle collection query results, see Section A ReportQuery a type of partial object query returns summary data for selected objects using the database reporting functions and features supported by your platform.

Although the report query returns data not objects , it does enable you to query the returned data and specify it at the object level. By default, a ReportQuery returns a collection see Section For more information see Section A stream is a view of a collection, which can be a file, a device, or a Vector.

A stream provides access to the collection, one element at a time in sequence. This makes it possible to implement stream classes in which the stream does not contain all the objects of a collection at the same time.

Large result sets can be resource-intensive to collect and process. To improve performance and give the client more control over the returned results, configure TopLink queries to use a cursor or stream.

Sessions provide query methods that lets you perform the object operations listed in Table Table Session Object Query Summary. These methods implicitly construct and execute a DatabaseQuery based on any of the following input parameters and return Object or Object collection:. Allowing an unverified SQL string to be passed into these methods makes your application vulnerable to SQL injection attacks. To access all configurable options to further refine and optimize a query, consider using a corresponding DatabaseQuery directly.

Read-object queries return the first instance of an Object that matches the specified selection criteria, and read-all object queries return all such instances. You can also pass in a domain Object with its primary key set and TopLink will construct and execute a read-object query to select that object. This is one form of query by example. For more information on query by example, see Section Oracle recommends that you create and update objects using a unit of work: doing so is the most efficient way to manage transactions, concurrency, and referential constraints.

However, you can also create and update objects using a session query. These session queries are a convenient way to modify objects directly on the database when you manage simple, nonbusiness object data that has no relationships for example, user preferences. If you know an object is new, you can use an insertObject method to avoid having TopLink perform an existence check.

If you do not know if an object is new, use the updateObject , writeObject , or writeAllObject methods: TopLink performs an existence check if necessary. When you execute a write session query, it writes both the object and its privately owned parts to the database. To manage this behavior, use a corresponding DatabaseQuery see Section Using the Session method deleteObject , you can delete a specific object. Using the Session method deleteAllObjects , you can delete a collection of objects.

Each specified object and all its privately owned parts are deleted. In the case of deleteAllObjects , all deletions are performed within a single transaction. All session types provide an executeQuery method that takes any of the following types of DatabaseQuery :.

Using an ObjectLevelReadQuery , you can query your data source and return Object instances that match the specified selection criteria. This section describes the following:. Using a ReadObjectQuery , you can query your data source and return the first object that matches the specified selection criteria. Using a ReadAllQuery , you can query your data source and return a Collection of all the objects that match the specified selection criteria.

By default, an ObjectLevelReadQuery returns all attributes of the objects read. If you require only certain attributes from selected objects, you can create a partial object query by using ObjectLevelReadQuery method addPartialAttributes. Using this method, you can improve query performance by making TopLink return objects with only specified attributes populated.

Applications frequently use partial object queries to compile a list for further selection. For example, a query to find the names and addresses of all employees over the age of 40 returns a list of data the names and addresses that partially represents objects the employees. A common next step is to present this list so the user can select the required object or objects from the list. Later retrieval of a complete object is simplified because TopLink always includes the primary key attribute even if you do not add it as a partial attribute.

If you require only summary information for certain attributes from selected objects, it is more efficient to use a ReportQuery see Section In cases where you know that data is read-only, you can improve performance by specifying a query as read-only: this tells TopLink that any object returned by the query is immutable.

Section Join reading is a query optimization feature that allows a single query for a class to return the data to build the instances of that class and its related objects. Use this feature to improve query performance by reducing database access. By default, relationships are not join-read: each relationship is fetched separately when accessed if you are using indirection lazy loading or as a separate database query if you are not using indirection.

Join reading is not currently supported for any other relationship mappings. Table Join Reading by Mapping Type. Direct collection see Section Aggregate collection see Section Join reading can specify multiple and nested relationships to be joined. Nested joins are expressed through using expressions see Section Outer joins can also be used with join reading through using the expression outer join API. If an outer join is not used, objects with missing one-to-one relationships or empty one-to-many relationships will be filtered from the result set.

You can also configure an object-level read query to allow inherited subclasses to be outer-joined to avoid the cost of a single query per class. You can also specify inner or outer joins using the useInnerJoinFetch or useOuterJoinFetch method of any of the mappings listed in Table You can use join reading with custom SQL or stored procedures, but the query must ensure that all of the required data to build all of the join-read objects is returned.

If the result set includes the same tables or fields, they must be returned in the same table order as TopLink would have generated. TopLink provides two main methods for expressions that query for data: getField and getTable.

The getField method lets you retrieve data from either an unmapped table or an unmapped field from an object. In either case, the field must be part of a table represented by that object's class; otherwise, TopLink raises an exception when you execute the query. You can also use the getField method to retrieve the foreign key information for an object. Example illustrates how to use the data expression method operator getField with an object.

Example Using getField with an Object. The getTable method returns an expression that represents an unmapped table in the database. This expression provides a context from which to retrieve an unmapped field when you use the getField method.

Example illustrates how to combine both getField and getTable in the same expression. Example Using getTable and getField Together. A common use for the getTable and getField methods is to retrieve information from a link table or reference table that supports a manyEtoEmany relationship. Example reads a many-to-many relationship that uses a link table and also checks an additional field in the link table.

This code combines an object query with a data query, using the employee's manager as the basis for the data query. It also features parameterization for the project ID. Use Java code to create more complex expressions and to take full advantage of the features in the expressions API see Section To create TopLink expressions for named queries, use this procedure:.

From the Named Queries Format tab, click Edit or double-click a query string. The Expression Builder dialog box appears. Figure Expression Builder Dialog Box. Figure numbered callouts identify the following user-interface components:. Click Add or Add Nested to create a new expression. TopLink assigns a sequence number to each node and nested node. Literal —Select the Type and enter a literal value for Value. Query Key —Click Edit and select the query key.

Parameter —Click Add to add a new parameter and then select from the list. Click OK. TopLink Workbench adds the expression to the Named Queries tab. Each expression contains elements arguments to evaluate. Expressions using the Is Null or Not Null operators require only a single argument. Select an existing expression or click Add or Add Nested to add a new expression to the named query.

For the First Argument , click Edit. The Choose Query Key dialog box appears. Select the attribute, specify if the query allows a null value, and click OK. Use the Allows Null and Allows None options to define an expression with an outer join. For more information, see Section Use the Operator list to specify how TopLink should evaluate the expression.

For Literal arguments, choose the literal type such as String or Integer and enter the literal value. For Query Key arguments, click Edit. The Choose Query Key dialog box appears see step 3 and Figure For Parameter arguments, click Add to add a parameter and then use the list to select it. Example Sample Expression.

To create an expression in Java code, use the Expression class or ExpressionBuilder method get. The ExpressionBuilder acts as a substitute for the objects that you query. To construct a query, call methods on the ExpressionBuilder that correspond to the attributes of the objects.

We recommend that you name ExpressionBuilder objects according to the type of objects against which you do a query. Example illustrates how to create a complex expression by combining two smaller expressions with a logical and operator. Example illustrates how to create an expression using the notLike operator.

Different databases sometimes implement the same functions in different ways. To manage differences, TopLink recognizes functions and other operators that vary according to the relational database. Although most platform-specific operators exist in TopLink, if necessary, you can create your own operators.

The selector is the identifier id by which users refer to the function. The strings are the constant strings used in printing the function. When printed, the strings alternate with the function arguments. You can also specify whether the operator is prefix or postfix. In a prefix operator, the first constant string prints before the first argument; in a postfix, it prints afterwards. Where you create a user-defined function and how you add it to the TopLink expression framework depends on whether you want the new function available to all database platforms or to only a specific database platform.

To make the function that overrides a specific operation on your own platform, use the following procedure:. Create a subclass of the desired DatabasePlatform from oracle. Podcast Making Agile work for data science. Featured on Meta. New post summary designs on greatest hits now, everywhere else eventually. Related Hot Network Questions. Question feed. Stack Overflow works best with JavaScript enabled. In EclipseLink, a custom sequence generator can be implemented and registered by using the GeneratedValue annotation.

The following sections describe how to convert various Hibernate annotations to EclipseLink annotations. In Hibernate, the ForeignKey annotation allows you to define the name of the foreign key to be used during schema generation. EclipseLink does generate reasonable names for foreign keys, but does not provide an annotation or eclipselink-orm.

When migrating, the recommended solution is to have EclipseLink generate the schema DDL commands to a script file instead of directly on the database. The script can then be customized to use different names prior to being executed. The foreign key name is not used by EclipseLink at runtime, but is required if EclipseLink attempts to drop the schema.

In this case, the drop script should be generated to a file and customized to match the foreign key names used during creation. In Hibernate, the Cache annotation configures the caching of entities and relationships.

Because EclipseLink uses an entity cache instead of a data cache, the relationships are automatically cached. In these cases, the Cache annotation should be removed during migration. When the Cache annotation is used on an entity, its behavior is similar to the EclipseLink Cache annotation. For more information about the Cache annotation and equivalent eclipselink-orm. The persistence. It specifies the persistence units, and declares the managed persistence classes, the object-relational mapping, and the database connection details.

Example illustrates a persistence. Hibernate-specific values appear in bold font. Key differences include the value for the persistence provider. For EclipseLink, this value is org. The names of EclipseLink-specific properties are typically be prefixed by eclipselink , for example, eclipselink.