Jpa join fetch multiple tables

Hibernate Tips is a series of posts in which I describe a quick and easy solution for common Hibernate questions. If you have a question for a future Hibernate Tip, please post a comment below.

So, the question I want to answer today is:. They tell Hibernate which database tables it shall join in the generated SQL query and how it shall do that. Unfortunately, the Criteria API is not as easy to use as most of us would prefer.

Defining a JOIN clause is pretty simple. You first call the from method on your CriteriaQuery object to get a Root object. In the next step, you can call the join method to define your JOIN clause based on a managed association. In the following example, the books attribute of the Author entity models a many-to-many association to the Book entity.

The only difference is that you need to provide a JoinType as the second parameter to the join method. The best way to do that is to create a query that returns Tuple instances. You can then call the multiselect method to select Author and Book entities. The returned Tuple interface provides a comfortable way to process the result of your query. You need to call the fetch method instead.

JPA Tutorial - JPA ManyToOne Two Join Columns Example

The second big difference is the return type of the fetch method. The returned Fetch interface is very similar to the Join interface. As a workaround, you can cast the Fetch interface to a Join interface. Even so, the interfaces are independent of each other; this approach works with Hibernate and EclipseLink. This is the important difference to a standard JOIN clause. The executed query is identical to the previous example.Posted on October 22, by vladmihalcea.

In our example, we need to load a Forest with its Trees and Branches and Leaves, and we will try to see have Hibernate behaves for three collection types: Sets, Indexed Lists, and Bags. If you want to learn the best way to fix the MultipleBagFetchExceptionthen check out this article. So, my solution is to simply get the lowest level of children and fetch all needed associations all the way up the entity hierarchy. The EntityGraphBuilder is one utility I wrote that takes an array of EntityVisitor objects and applies them against the visited objects.

This goes recursively up to the Forest object, and we are replacing the Hibernate collections with new ones, adding each child to the parent-children collection. This code is packed as a utility, and the customization comes through extending the EntityVisitors like this:. If you enjoyed this article, I bet you are going to love my Book and Video Courses as well. This is not the Visitor pattern per sebut it has a slight resemblance to it. Code available on GitHub.

For example, we have a Division entity that contains other Divisions.

Hibernate Tips: What’s the Difference between JOIN, LEFT JOIN and JOIN FETCH

You can use Recursive CTE for that. What if your child-entities do not have a link to a parent? Check out my High-Performance Java Persistence book for more details. Your email address will not be published. Notify me of follow-up comments by email. This site uses Akismet to reduce spam. Learn how your comment data is processed.

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Save Your Seat!Hibernate Tips is a series of posts in which I describe a quick and easy solution for common Hibernate questions.

jpa join fetch multiple tables

If you have a question for a future Hibernate Tip, please leave a comment below. Is there any way to do that with JPA or Hibernate? Here are the 2 tables:. The SecondaryTable annotation specifies the second database table to which the entity gets mapped. You need to annotate the attributes that map these columns with an additional Column annotation that provides the name of the secondary table.

And when you read an Author entity, Hibernate gets the attribute values from the same 2 tables. As you can see in the log outputHibernate uses the name and value of the primary key column of the primary table also as the name and value of the primary key column of the secondary table. By default, Hibernate uses an identical mapping to map the primary key attribute to both tables.

You can do that with the pkJoinColumns attribute of the SecondaryTable annotation. If you enjoyed this post, you might also be interested in the following posts about entity mappings:. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. Join the free Thoughts on Java Library to get access to lots of member-only content, like a printable PDF for this post, lots of cheat sheets and 2 ebooks about Hibernate.

Join Now! Already a member? Login here. Get more recipes like this one in my new book Hibernate Tips: More than 70 solutions to common Hibernate problems.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information.

I'm trying to create a criteria to retrieve some objects from 3 tables Associate, Update and Detail. My objective is to retrieve a list of Updates that has at least a Detail with null value in a specified field, given an Associate id. In JPQL was easy to do but the client said that this must be coded with criteria. Each join takes you from the leftish type parameter to the rightish one.

From that, you can build other joins. Try this code not tested :. Checkout this test with even more than three tables. Also use static meta model instead of using direct attribute names.

Learn more. Asked 6 years, 10 months ago. Active 1 year, 2 months ago.

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Viewed 39k times. I searched but can't find any example with 3 entities.

JPA Tutorial - JPA Query Join Fetch Example

Rafael Toledo Rafael Toledo 4, 4 4 gold badges 17 17 silver badges 32 32 bronze badges. Active Oldest Votes. Worked like a charm!By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service. The dark mode beta is finally here. Change your preferences any time.

Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. Learn more. Asked 4 days ago. Active 4 days ago.

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Linked 1. Related Hot Network Questions. Question feed. Stack Overflow works best with JavaScript enabled.Hibernate Tips is a series of posts in which I describe a quick and easy solution for common Hibernate questions.

If you have a question for a future Hibernate Tip, please leave a comment below. What are the differences between these 3 join statements?

jpa join fetch multiple tables

It supports clauses with the same name and a very similar syntax. Your persistence provider, e. You can define a join condition that specifies which rows of each table shall be joined with each other.

How to fetch entities multiple levels deep with Hibernate

In most cases, this condition compares the values of a primary key column of one table with the values of a foreign key column of an associated table. But you can also define more complex conditions using multiple columns of both tables.

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In JPQL, you need to define join statements based on association mappings. This mapping provides the names of the foreign key and primary key columns. It uses the defined many-to-many association to join the Author table with the association table BookAuthor. It then joins the association table with the Book table.

If the database contains a Book for a specific Authorthe query returns it as the second element in the Object[]. Otherwise, that array element is null. The second element of the Object[] would never be null. Hibernate generates the following SQL statement for this query. It selects all columns mapped by the Author and Book entities and uses the defined association to create a left join between the Book and the Author tables. It tells the persistence provider to not only join the 2 database tables within the query but to also initialize the association on the returned entity.

Hibernate then maps the result set to Author and Book entities. It uses the Book entities to initialize the books attribute of each Author entity before it returns a List of Author entities. If the database contains a Book for a specific Author, the query returns it as the second element in the Object[]. So, the second element of the Object[] the one which contains the Bookswill never be null. Your email address will not be published.

Save my name, email, and website in this browser for the next time I comment. This site uses Akismet to reduce spam. Learn how your comment data is processed. Join the free Thoughts on Java Library to get access to lots of member-only content, like a printable PDF for this post, lots of cheat sheets and 2 ebooks about Hibernate.

jpa join fetch multiple tables

Join Now! Already a member? Login here. Get more recipes like this one in my new book Hibernate Tips: More than 70 solutions to common Hibernate problems.

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It gives you more than 70 ready-to-use recipes for topics like basic and advanced mappings, logging, Java 8 support, caching and statically and dynamically defined queries.

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Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I was wrote query like below:.

I found articles about this error, but these articles only describe situation where in one entity are two collections to join. My problem is a little different and I don't know How to solve it. You can use a Child-Parent fetch strategy and recombine the entity tree from the result.

Learn more. Asked 4 years, 11 months ago. Active 1 year ago. Viewed 53k times. But I got the error org. MultipleBagFetchException: cannot simultaneously fetch multiple bags I found articles about this error, but these articles only describe situation where in one entity are two collections to join.

It is possible to do in one query? Sorry for my bad english, but I usually speak in other language. Vlad Mihalcea Zaprogramowany Zaprogramowany 1 1 gold badge 5 5 silver badges 10 10 bronze badges.

Active Oldest Votes. Vlad Mihalcea Vlad Mihalcea How to create indexed list? That's the subject of another question, which I'm sure it's already answered on SO.

jpa join fetch multiple tables

Nicholas Aug 24 '18 at It works like a charm with Hibernate. What JPA provider are you using? There's just one problem, your query returns a post and no category.

Mar 15 '19 at Govind Singh 13k 11 11 gold badges 55 55 silver badges 91 91 bronze badges. This does not have a fetch so it will not initialized the joined collections. This response has no bearing in this context.