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This article is part of a series of posts related to calling various relational database systems stored procedures and database functions from Hibernate. The reason for writing this down is because there are many peculiarities related to the underlying JDBC driver support and not every JPA or Hibernate feature is supported on every relational database.
MySQL supports both stored procedures and functions, so first we’ll start with the following stored procedure that outputs a simple value.
CREATE PROCEDURE count_comments (
IN postId INT,
OUT commentCount INT
)
BEGIN
SELECT COUNT(*) INTO commentCount
FROM post_comment
WHERE post_comment.post_id = postId;
END
This stored procedure has two parameters: an input parameter (e.g. postId) and an output parameter (e.g. commentCount) which is used to return the count of post_comment records associated with a given post_id parent row.
To call this stored procedure, you can use the following Java Persistence API 2.1 syntax:
StoredProcedureQuery query = entityManager
.createStoredProcedureQuery("count_comments")
.registerStoredProcedureParameter(
"postId",
Long.class,
ParameterMode.IN
)
.registerStoredProcedureParameter(
"commentCount",
Long.class,
ParameterMode.OUT
)
.setParameter("postId", 1L);
query.execute();
Long commentCount = (Long) query
.getOutputParameterValue("commentCount");
By default, the underlying JDBC
CallableStatementremains open even after executing the stored procedure and fetching theOUTorREF_CURSORparameters.To explicitly close the
CallableStatement, you have to callreleaseon the underlyingProcedureOutputsobject as illustrated in the following example:StoredProcedureQuery query = entityManager .createStoredProcedureQuery("count_comments") .registerStoredProcedureParameter( "postId", Long.class, ParameterMode.IN ) .registerStoredProcedureParameter( "commentCount", Long.class, ParameterMode.OUT ) .setParameter("postId", 1L); try { query.execute(); Long commentCount = (Long) query .getOutputParameterValue("commentCount"); assertEquals(Long.valueOf(2), commentCount); } finally { query.unwrap(ProcedureOutputs.class) .release(); }For more details, check out this article.
A stored procedure can also define a REFCURSOR output parameter which is associated with a database cursor that can be iterated to fetch multiple database records:
CREATE PROCEDURE post_comments(IN postId INT)
BEGIN
SELECT *
FROM post_comment
WHERE post_id = postId;
END
When trying to call this stored procedure:
StoredProcedureQuery query = entityManager
.createStoredProcedureQuery("post_comments")
.registerStoredProcedureParameter(
1,
Long.class,
ParameterMode.IN
)
.registerStoredProcedureParameter(
2,
Class.class,
ParameterMode.REF_CURSOR
)
.setParameter(1, 1L);
query.execute();
List<Object[]> postComments = query.getResultList();
Hibernate throws the following exception:
org.hibernate.QueryException: java.lang.IllegalArgumentException: org.hibernate.QueryException: Dialect [org.hibernate.dialect.MySQL57InnoDBDialect] not known to support REF_CURSOR parameters
Even though this stored procedure is working properly on Oracle and PostgreSQL, on MySQL, it does not work because the MySQL driver does not support REFCURSOR outside of stored procedure.
However, instead of using a REFCURSOR parameter, you can simply use the returned ResultSet:
StoredProcedureQuery query = entityManager
.createStoredProcedureQuery("post_comments");
query.registerStoredProcedureParameter(
1,
Long.class,
ParameterMode.IN
);
query.setParameter(1, 1L);
List<Object[]> postComments = query.getResultList();
MySQL also supports database functions, which, unlike stored procedures, don’t use input and output parameters, but one or more function arguments and a single return value.
The first stored procedure can be turned into a function which looks like this:
CREATE FUNCTION fn_count_comments(postId integer)
RETURNS integer
DETERMINISTIC
READS SQL DATA
BEGIN
DECLARE commentCount integer;
SELECT COUNT(*) INTO commentCount
FROM post_comment
WHERE post_comment.post_id = postId;
RETURN commentCount;
END
Unfortunately, as of writing (Hibernate 5.2.4), both the Java Persistence 2.1 stored procedure and the Hibernate-specific API cannot be used to call functions.
However, there are several workarounds for this limitations.
Fortunately, we can call the database function using plain JDBC API:
int commentCount = session.doReturningWork(connection -> {
try (CallableStatement function = connection.prepareCall(
"{ ? = call fn_count_comments(?) }")) {
function.registerOutParameter(1, Types.INTEGER);
function.setInt(2, 1);
function.execute();
return function.getInt(1);
}
});
If you enjoyed this article, I bet you are going to love my Book and Video Courses as well.
Calling stored procedures and functions is not difficult at all, but it requires knowing some details about Hibernate and the underlying JDBC driver capabilities. Hibernate 6.0 aims to revamp the SQL function support, so stay tuned!
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