Spring Data JDBC uses implementations of the interface Dialect to encapsulate behavior that is specific to a database or its JDBC driver. By default, the AbstractJdbcConfiguration tries to determine the database in use and register the correct Dialect. This behavior can be changed by overwriting jdbcDialect(NamedParameterJdbcOperations).

If you use a database for which no dialect is available, then your application won’t startup. In that case, you’ll have to ask your vendor to provide a Dialect implementation. Alternatively, you can:

The properties of the following types are currently supported:

The handling of referenced entities is limited. This is based on the idea of aggregate roots as described above. If you reference another entity, that entity is, by definition, part of your aggregate. So, if you remove the reference, the previously referenced entity gets deleted. This also means references are 1-1 or 1-n, but not n-1 or n-m.

If you have n-1 or n-m references, you are, by definition, dealing with two separate aggregates. References between those may be encoded as simple id values, which map properly with Spring Data JDBC. A better way to encode these is to make them instances of AggregateReference. An AggregateReference is a wrapper around an id value which marks that value as a reference to a different aggregate. Also, the type of that aggregate is encoded in a type parameter.

When you use the standard implementations of CrudRepository that Spring Data JDBC provides, they expect a certain table structure. You can tweak that by providing a NamingStrategy in your application context.

When the NamingStrategy does not matching on your database table names, you can customize the names with the @Table annotation. The element value of this annotation provides the custom table name. The following example maps the MyEntity class to the CUSTOM_TABLE_NAME table in the database:

When the NamingStrategy does not matching on your database column names, you can customize the names with the @Column annotation. The element value of this annotation provides the custom column name. The following example maps the name property of the MyEntity class to the CUSTOM_COLUMN_NAME column in the database:

The @MappedCollection annotation can be used on a reference type (one-to-one relationship) or on Sets, Lists, and Maps (one-to-many relationship). idColumn element of the annotation provides a custom name for the foreign key column referencing the id column in the other table. In the following example the corresponding table for the MySubEntity class has a NAME column, and the CUSTOM_MY_ENTITY_ID_COLUMN_NAME column of the MyEntity id for relationship reasons:

When using List and Map you must have an additional column for the position of a dataset in the List or the key value of the entity in the Map. This additional column name may be customized with the keyColumn Element of the @MappedCollection annotation:

Embedded entities are used to have value objects in your java data model, even if there is only one table in your database. In the following example you see, that MyEntity is mapped with the @Embedded annotation. The consequence of this is, that in the database a table my_entity with the two columns id and name (from the EmbeddedEntity class) is expected.

However, if the name column is actually null within the result set, the entire property embeddedEntity will be set to null according to the onEmpty of @Embedded, which nulls objects when all nested properties are null.
Opposite to this behavior USE_EMPTY tries to create a new instance using either a default constructor or one that accepts nullable parameter values from the result set.

If you need a value object multiple times in an entity, this can be achieved with the optional prefix element of the @Embedded annotation. This element represents a prefix and is prepend for each column name in the embedded object.

Embedded entities containing a Collection or a Map will always be considered non empty since they will at least contain the empty collection or map. Such an entity will therefore never be null even when using @Embedded(onEmpty = USE_NULL).

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Spring Data JDBC uses the ID to identify entities. The ID of an entity must be annotated with Spring Data’s @Id annotation.

When your data base has an auto-increment column for the ID column, the generated value gets set in the entity after inserting it into the database.

One important constraint is that, after saving an entity, the entity must not be new any more. Note that whether an entity is new is part of the entity’s state. With auto-increment columns, this happens automatically, because the ID gets set by Spring Data with the value from the ID column. If you are not using auto-increment columns, you can use a BeforeConvert listener, which sets the ID of the entity (covered later in this document).

Spring Data JDBC supports optimistic locking by means of a numeric attribute that is annotated with @Version on the aggregate root. Whenever Spring Data JDBC saves an aggregate with such a version attribute two things happen: The update statement for the aggregate root will contain a where clause checking that the version stored in the database is actually unchanged. If this isn’t the case an OptimisticLockingFailureException will be thrown. Also the version attribute gets increased both in the entity and in the database so a concurrent action will notice the change and throw an OptimisticLockingFailureException if applicable as described above.

This process also applies to inserting new aggregates, where a null or 0 version indicates a new instance and the increased instance afterwards marks the instance as not new anymore, making this work rather nicely with cases where the id is generated during object construction for example when UUIDs are used.

During deletes the version check also applies but no version is increased.

The JDBC module supports defining a query manually as a String in a @Query annotation or as named query in a property file.

Deriving a query from the name of the method is is currently limited to simple properties, that means properties present in the aggregate root directly. Also, only select queries are supported by this approach.

The following example shows how to use @Query to declare a query method:

For converting the query result into entities the same RowMapper is used by default as for the queries Spring Data JDBC generates itself. The query you provide must match the format the RowMapper expects. Columns for all properties that are used in the constructor of an entity must be provided. Columns for properties that get set via setter, wither or field access are optional. Properties that don’t have a matching column in the result will not be set. The query is used for populating the aggregate root, embedded entities and one-to-one relationships including arrays of primitive types which get stored and loaded as SQL-array-types. Separate queries are generated for maps, lists, sets and arrays of entities.

If no query is given in an annotation as described in the previous section Spring Data JDBC will try to locate a named query. There are two ways how the name of the query can be determined. The default is to take the domain class of the query, i.e. the aggregate root of the repository, take its simple name and append the name of the method separated by a .. Alternatively the @Query annotation has a name attribute which can be used to specify the name of a query to be looked up.

Named queries are expected to be provided in the property file META-INF/jdbc-named-queries.properties on the classpath.

The location of that file may be changed by setting a value to @EnableJdbcRepositories.namedQueriesLocation.

The easiest way to properly plug MyBatis into Spring Data JDBC is by importing MyBatisJdbcConfiguration into you application configuration:

As you can see, all you need to declare is a SqlSessionFactoryBean as MyBatisJdbcConfiguration relies on a SqlSession bean to be available in the ApplicationContext eventually.

For each operation in CrudRepository, Spring Data JDBC runs multiple statements. If there is a SqlSessionFactory in the application context, Spring Data checks, for each step, whether the SessionFactory offers a statement. If one is found, that statement (including its configured mapping to an entity) is used.

The name of the statement is constructed by concatenating the fully qualified name of the entity type with Mapper. and a String determining the kind of statement. For example, if an instance of org.example.User is to be inserted, Spring Data JDBC looks for a statement named org.example.UserMapper.insert.

When the statement is run, an instance of [MyBatisContext] gets passed as an argument, which makes various arguments available to the statement.

The following table describes the available MyBatis statements:

Spring Data JDBC uses the EntityCallback API for its auditing support and reacts on the following callbacks:

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The following example shows an implementation of a Converter that converts from a Boolean object to a String value:

There are a couple of things to notice here: Boolean and String are both simple types hence Spring Data requires a hint in which direction this converter should apply (reading or writing). By annotating this converter with @WritingConverter you instruct Spring Data to write every Boolean property as String in the database.

The following example shows an implementation of a Converter that converts from a String to a Boolean value:

There are a couple of things to notice here: String and Boolean are both simple types hence Spring Data requires a hint in which direction this converter should apply (reading or writing). By annotating this converter with @ReadingConverter you instruct Spring Data to convert every String value from the database that should be assigned to a Boolean property.

Value conversion uses JdbcValue to enrich values propagated to JDBC operations with a java.sql.Types type. Register a custom write converter if you need to specify a JDBC-specific type instead of using type derivation. This converter should convert the value to JdbcValue which has a field for the value and for the actual JDBCType.

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To let your query methods be transactional, use @Transactional at the repository interface you define, as the following example shows:

Typically, you want the readOnly flag to be set to true, because most of the query methods only read data. In contrast to that, deleteInactiveUsers() uses the @Modifying annotation and overrides the transaction configuration. Thus, the method is with the readOnly flag set to false.

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