Native query return entity relationship

Chapter Native SQL Queries

native query return entity relationship

Creating a dynamic native query is quite simple. The EntityManager interface provides a method called createNativeQuery for it. This method returns an. Doctrine Object Relational Mapper Documentation: Native SQL. entity result describes an entity type that appears as a joined relationship element in the .. This mapping returns 2 entities, User and Address, each property is declared and . How to map a JPA @ManyToOne relationship to a SQL query using the Hibernate @JoinFormula return doInJPA(entityManager -> {.

What this means in practice is that you won't be able to pass p. However, there are ways to work around this issue. In the following example, you define class LineItemSum whose constructor is then used in the select list of the query, taking p. What the LineItemSum constructor does is multiply p. Next, you can iterate through the LineItemSum list retrieved by the query, summing the values of the LineItemSum's rslt variable.

The following snippet shows how all this can be implemented in code: In most cases, however, you will have to deal with queries that receive an instance or a list of instances of a certain entity. Retrieved Entity Instances and the Current Persistence Context The query results in the article examples so far have been simply printed out. In real-world applications, though, you may need to perform some further operations on the query results.

For example, you may need to update the retrieved instances and then persist them back to the database. This raises the question: In particular, it would be interesting to learn in what state, concerning the current persistence context, retrieved entity instances are. If you have some experience with Java Persistence, you should know what a persistence context is.

To recap, a persistence context is a set of entity instances managed by the EntityManager instance associated with that context.

Querying JPA Entities with JPQL and Native SQL

Actually, the EntityManager API includes more than twenty methods to manage the lifecycle of entity instances, control transactions, and create instances of Query whose methods are then used to execute the query specified and retrieve the query result.

With respect to a persistence context, an entity instance can be in one of the following four states: Using an appropriate EntityManager's method, you can change the state of a certain entity instance as needed. It's interesting to note, however, that only instances in managed state are synchronized to the database, when flushing to the database occurs.

To be precise, the entity instances in the removed state are also synchronized, meaning the database records corresponding to those instances are removed from the database. By contrast, instances in the new or detached state won't be synchronized to the database.

native query return entity relationship

For example, if you create a new PurchaseOrder instance and then invoke the EntityManager's flush method, another record will not appear in the purchaseOrders table to which the PurchaseOrder entity is mapped. This is because that new PurchaseOrder instance has not been attached to the persistence context. Here is what the code might look like: To fix the problem, you need to invoke the EntityManager's persist method for the new PurchaseOrder instance before invoking the flush, as shown in the following example: Alternatively, provided you've set the cascade option to PERSIST or ALL when defining the relationship with PurchaseOrder in the Customer entity, you might add the newly created PurchaseOrder instance to the list of the orders associated with the customer instance, replacing the persist operation with the following: According to the JPA specification, regardless of the way you retrieve entities—whether it is the EntityManager's find method or a query—they are automatically attached to the current persistence context.

This means entity instances retrieved by a JPQL query become automatically managed.

The best way to map a projection query to a DTO (Data Transfer Object) with JPA and Hibernate

You can, for example, change the value of a retrieved instance's field and then synchronize that change to the database by invoking the EntityManager's flush method or committing the current transaction.

You don't need to worry about the state of the instances associated with the retrieved instances either. The fact is that the first time you access an associated instance it becomes managed automatically.

Here is a simple example showing how all this works in practice: Note that you don't invoke the persist method for the retrieved PurchaseOrder instance, nor for its related OrderLineItem instance being modified here.

  • Native Queries – How to call native SQL queries with JPA
  • Querying JPA Entities with JPQL and Native SQL
  • Hibernate Tips: How to map native query results to entities

In spite of this fact, the changes made to the first line item in the order will be persisted to the database upon committing the transaction. This happens because both the retrieved entity instances and their associations are automatically attached to the current persistence context.

native query return entity relationship

As mentioned earlier, the former become managed when they are retrieved, and the latter are attached to the context as you access them. In some situations, you may want associations to be attached to the context upon the query execution, rather than upon the first access.

Say, you want to obtain all the orders belonging to a certain customer, upon retrieving that customer instance. This approach guarantees you're dealing with the customer orders available at the time of query execution. If, for example, a new order is added to another context and then synchronized to the database before you first time access the orders list associated with the customer instance retrieved, you won't see this change until you refresh the state of the customer instance from the database.

Being not part of the explicit query result, the PurchaseOrder entity instances associated with the Customer instance retrieved here are also retrieved and attached to the current persistence context upon the query execution. The most important thing to understand about native SQL queries created with EntityManager methods is that they, like JPQL queries, return entity instances, rather than database table records.

Here is a simple example of a dynamic native SQL query: Among other things, the above example illustrates that you can bind arguments to native query parameters. In particular, you can bind arguments to positional parameters in the same way as if you were dealing with a JPQL query. The main disadvantage of native queries is complexity of result binding.

In the example, the query produces a single result of a simple type, thus avoiding this problem. In practice, however, you often have to deal with a result set of a complex type.

In this case, you will have to declare an entity to which you can map your native query, or define a complex result set mapped to multiple entities or to a blend of entities and scalar results. Using Stored Procedures Another disadvantage of native queries is that your Java code becomes directly dependent on the underlying database structure.

To work around this problem, while still using native queries, you might take advantage of stored procedures, moving complex SQL queries into programs stored and executed inside the database, and then calling those stored programs instead of making direct calls to the underlying tables. What this means in practice is that stored procedures may save you the trouble of dealing with the underlying tables directly from the queries that are hard-coded in your Java code.

The benefit to this approach is that in most cases you won't need to modify your Java code to follow the changes in the underlying database structure. Instead, only the stored procedures will need fixing. Turning back to the example discussed in the preceding section, you might move the complex join query used there into a stored function, created as follows: This is done via the addJoin method, which allows you to join in an association or collection.

[email protected] annoatation in Spring data JPA with Native Query(SQL query)

Notice that you added an alias name "cat" to be able to specify the target property path of the join. It is possible to do the same eager joining for collections, e. Returning multiple entities Until now, the result set column names are assumed to be the same as the column names specified in the mapping document.

This can be problematic for SQL queries that join multiple tables, since the same column names can appear in more than one table. Column alias injection is needed in the following query which most likely will fail: The query will, however, fail because there is a conflict of names; the instances are mapped to the same column names.

Also, on some databases the returned column aliases will most likely be on the form "c. The following form is not vulnerable to column name duplication: Alternatively, you can list the columns explicitly, but even in this case Hibernate injects the SQL column aliases for each property. The placeholder for a column alias is just the property name qualified by the table alias. You can even use the property aliases in the where clause.

Alias and property references In most cases the above alias injection is needed. For queries relating to more complex mappings, like composite properties, inheritance discriminators, collections etc.