one-to-many

问题 I have the data model you can see below, and a nested SUBQUERY predicate, but in somehow it just not works. Any idea how to correct it? I figured out, this here down is working finally: [NSPredicate predicateWithFormat:@"SUBQUERY(bs, $B, SUBQUERY($B.cs, $C, $C.ds.name != \"xxx\").@count > 0).@count > 0"]; 回答1: Ok, so here is the working solution: [NSPredicate predicateWithFormat:@"SUBQUERY(bs, $B, SUBQUERY($B.cs, $C, $C.ds.name != \"xxx\").@count > 0).@count > 0"]; 来源： https://stackoverflow

问题 I've got some problem with hibernate @OneToMany mapping. It goes like here @Entity @Table(name = "albums") @SequenceGenerator(name = "ALBUMS_SEQ", sequenceName = "albums_seq", allocationSize = 1) public class AlbumDs { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "ALBUMS_SEQ") private Integer id; private Integer ownerId; private String name; private String description; private Date created; @OneToMany(cascade = CascadeType.ALL) @JoinColumn(name = "albumId", insertable =

问题 There is the possibility to disable the @OneToMany relationship join table with the @JoinColumn annotation. The default is a join table. What are the advantages and disadvantages for a production system for example? When should I use a join table and when not? Thank you. 回答1: By default @OneToMany will create a join table only if you'll use unidirectional relationship . In other words, if you have Employee and Project entities and the Employee entity is defined as follows (assume there is no

问题 i have a Question about referencing ParentEntities from Child Entites ir If i have something like this: Parent.java: @Entity(name ="Parent") public class Parent { @Id @Generate..... @Column private int id; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "parent") private Set<Child> children; simple ... getter and setter ... } And the Child.java: @Entity(name ="Child") public class Child{ @Id @Generate.... @Column private int id; @ManyToOne private Parent parent; ...

问题 i have a Question about referencing ParentEntities from Child Entites ir If i have something like this: Parent.java: @Entity(name ="Parent") public class Parent { @Id @Generate..... @Column private int id; @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.LAZY, mappedBy = "parent") private Set<Child> children; simple ... getter and setter ... } And the Child.java: @Entity(name ="Child") public class Child{ @Id @Generate.... @Column private int id; @ManyToOne private Parent parent; ...

问题 I'm trying to set up a relationship as follows. Each Master item has one or more Detail items: public class Detail { public virtual Guid DetailId { get; set; } public virtual string Name { get; set; } } public class Master { public virtual Guid MasterId { get; set; } public virtual string Name { get; set; } public virtual IList<Detail> Details { get; set; } } And Mappings: public class MasterMap : ClassMap<Master> { public MasterMap() { Id(x => x.MasterId); Map(x => x.Name); HasMany(x => x

问题 Stack I'm using JPA2.0 with Eclipselink 2.6.3 and Spring 4(JTA). Problem I'm trying to override the class A attribute with @OneToMany mapping in class B and class C (which is similar to class B ) so that I can change the target entity to class X and Z respectively while fetching results for class B. Class A has SINGLE_TABLE inheritance and class B & C are discriminator classes which is maintained by @classExtractor depending on some field value in class A. Class Z has TABLE_PER_CLASS

问题 Stack I'm using JPA2.0 with Eclipselink 2.6.3 and Spring 4(JTA). Problem I'm trying to override the class A attribute with @OneToMany mapping in class B and class C (which is similar to class B ) so that I can change the target entity to class X and Z respectively while fetching results for class B. Class A has SINGLE_TABLE inheritance and class B & C are discriminator classes which is maintained by @classExtractor depending on some field value in class A. Class Z has TABLE_PER_CLASS

问题 I'm writing a feature which calls for the records of my joining table to carry extra metadata ( Joining-Table with Metadata ). I've attempted to implement this in accordance with this section of the Doctrine documentation. See below for example Entity definitions. The challenge now is that getGroups and setGroups do not yield/set Group entities (& the same is true from the Group instance perspective), but they yield GroupUser entities. This adds a substantial delay to process of managing this

问题 I have been scratching my head over this for weeks now and I have no idea how to work my way around it. I have two tables: Author (author_code, author_number, author_name) author_code and author_number are primary keys Title (author_code, title_code, sequence, title_desc) title_code and sequence are primary keys Code: @Entity @IdClass(AuthorPK.class) @Table(name="Author") public class Author implements Serializable { @Id @Column(name="author_code") private long authorCode; @Id @Column(name=