[Draft] Using Blaze Persistence - vinhtbkit/bkit-kb GitHub Wiki

Introduction

Setup

Maven

    <dependency>
      <groupId>com.blazebit</groupId>
      <artifactId>blaze-persistence-integration-hibernate-6.2</artifactId>
      <version>${blaze-persistence.version}</version>
      <scope>runtime</scope>
    </dependency>
    <dependency>
      <groupId>com.blazebit</groupId>
      <artifactId>blaze-persistence-integration-spring-data-3.1</artifactId>
      <version>${blaze-persistence.version}</version>
      <scope>compile</scope>
    </dependency>

Usage Example

Pagination and count in one query

Fetching a collection with pagination and also fetch child collections in 1 query

Given the following Database relationship

---
title: Customer - Orders
---
erDiagram
    USER ||--o{ POST : has
    USER {
      string email
      string id PK
    }

    POST {
      string id PK
      string name
    }
  • The customer has one-to-many relationship to orders

Define Entities

@Entity
public class UserEntity {
  @Id
  private String id;
  private String email;

  @OneToMany(mappedBy = "user")
  private Set<PostEntity> posts;
}

@Entity
public class PostEntity {
  @Id
  private String id;
  private String title;

  @ManyToOne(fetch = FetchType.LAZY)
  private UserEntity user;
}

Define EntityView

  • EntityView: read-only projections of entity
@EntityView(UserEntity.class)
public interface UserEntityView {
  @IdMapping
  String getId();
  String getEmail();
  Set<PostEntityView> getPosts();
}

@EntityView(PostEntity.class)
public interface PostEntityView {
  @IdMapping
  String getId();
  String getTitle();
}

Query

First, need to enable it:

@EnableEntityViews
public class BlazeCteApplication {
// more code

  @Bean
  @Scope(ConfigurableBeanFactory.SCOPE_SINGLETON)
  @Lazy(false)
  // inject the criteria builder factory which will be used along with the entity view manager
  public EntityViewManager createEntityViewManager(CriteriaBuilderFactory cbf, EntityViewConfiguration entityViewConfiguration) {
    return entityViewConfiguration.createEntityViewManager(cbf);
  }
}

Query:

  private final EntityViewManager evm;

  public Page<UserEntityView> findAll(String email, Pageable pageable) {
    var res = evm.applySetting(EntityViewSetting.create(UserEntityView.class), cbf.create(em, UserEntity.class))
        .orderByAsc("id") // Blaze requires at least one sort by "id" field
        .pageBy(pageable.getPageNumber(), pageable.getPageSize(), "id") // "id" is used for grouping results 
        .getResultList();
    return new PageImpl<>(res, pageable, res.size());
  }

Selection fetch

Output

The actual query looks like this

    select
        u1_0.id,
        u1_0.email,
        p1_0.id,
        p1_0.title,
        (select
            count(*) 
        from
            usr u2_0) 
    from
        usr u1_0 
    left join
        post p1_0 
            on u1_0.id=p1_0.user_id 
    where
        u1_0.id in(select
            u3_0.id 
        from
            usr u3_0 
        order by
            u3_0.id fetch first 3 rows only) 
    order by
        u1_0.id

Using CTE (Common Table Expressions)

Keyset Pagination

QueryDSL integration

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