N+1 Select Issues with Hibernate Part 2: Solving n+1 select issues - - PowerPoint PPT Presentation

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N+1 Select Issues with Hibernate Part 2: Solving n+1 select issues - - PowerPoint PPT Presentation

Dec 21, 2022 24 likes •138 views

How to find and fix N+1 Select Issues with Hibernate Part 2: Solving n+1 select issues with @NamedEntityGraphs www.thoughts-on-java.org Course Structure Part 1: What is the n+1 select issue? How to find it in your project?

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SLIDE 1

How to find and fix N+1 Select Issues with Hibernate

Part 2: Solving n+1 select issues with @NamedEntityGraphs

www.thoughts-on-java.org

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SLIDE 2

Course Structure

  • Part 1:
  • What is the n+1 select issue?
  • How to find it in your project?
  • Part 2:
  • Solving n+1 select issues with @NamedEntityGraphs
  • Part 3:
  • Solving n+1 select issues with dynamic EntityGraphs

www.thoughts-on-java.org

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SLIDE 3

Application

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SLIDE 4

@NamedEntityGraph

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@NamedEntityGraph

  • Introduced in JPA 2.1
  • Declaratively defines a graph of entities which will be loaded
  • Graph is query independent

www.thoughts-on-java.org

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@NamedEntityGraph

  • Define a simple @NamedEntityGraph

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@NamedEntityGraph( name = "graph.AuthorBooksReviews", attributeNodes = @NamedAttributeNode(value = "books") )

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@NamedEntityGraph

  • Define a multi-level @NamedEntityGraph

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@NamedEntityGraph( name = "graph.AuthorBooksReviews", attributeNodes = @NamedAttributeNode(value = "books", subgraph = "books"), subgraphs = @NamedSubgraph( name = "books", attributeNodes = @NamedAttributeNode("reviews") ) )

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@NamedEntityGraph

  • Provide entity graph as a hint

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EntityGraph graph = this.em.getEntityGraph("graph.AuthorBooks"); this.em.createQuery("SELECT DISTINCT a FROM Author a") .setHint("javax.persistence.loadgraph", graph);

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@NamedEntityGraph

  • Fetch graph
  • Eager loading for all elements of the graph
  • Lazy loading for all other attributes
  • Load graph
  • Eager loading for all elements of the graph
  • Loads all other attributes with their defined FetchType
  • Hib

iber erna nate te alwa always ys uses es a a lo load ad grap aph

  • HHH-8776

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@NamedEntityGraph

  • Advantages
  • Query specific EAGER loading
  • Definition of the graph is independent of the query
  • Disadvantages
  • Creates cartesian product

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SLIDE 11

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