one-to-many

问题 I'm trying to implement One-to-Many relation between two tables using hibernate. Here is my code: @Entity public class Board { @Id @Column(name = "board_id") @GeneratedValue private long id; @Column private String owner; @Column private String title; @Column private String refresh; @Column private Timestamp createDate; @Column private Timestamp modifyDate; @OneToMany(mappedBy="board", cascade=CascadeType.ALL) private List<Item> items; public long getId() { return id; } public void setId(long

问题 I'm trying to implement One-to-Many relation between two tables using hibernate. Here is my code: @Entity public class Board { @Id @Column(name = "board_id") @GeneratedValue private long id; @Column private String owner; @Column private String title; @Column private String refresh; @Column private Timestamp createDate; @Column private Timestamp modifyDate; @OneToMany(mappedBy="board", cascade=CascadeType.ALL) private List<Item> items; public long getId() { return id; } public void setId(long

问题 I am using spring boot to create a REST API. In this API, I have a One to Many relationship between check-in and Guests . I created a controller for check-in and use that save function of spring JPA. The save method is updating both checkin and guest tables but for the guest table, the check-in foreign key in the guests table is not getting added instead showing as null. Please someone help me. I need to create both guests and checkin simultaneously. Check-in Model @Data @Entity public class

问题 I have three collections: parent, child1, child2. parent collection: [{_id:1}, {_id:2}, {_id:3}] child1 collection: [{_id:1, child1:'a', parent:1}, {_id:2, child1:'b', parent:1}, {_id:3, child1:'c', parent:2}] child2 collection: [{_id:1, child1:'d', parent:2}, {_id:2, child1:'e', parent:3}] collections child1 and child2 referenced to parent collection. now, I want a query in mongoose to get a result like this: [ { _id:1, child1:[{_id:1, child1:'a'}, {_id:2, child1:'b'}], child2:[], }, { _id:2

问题 I develop web application with Entity framework 6. I have a model Folder that contains a list of Letter object. My letter object: public class Letter { [Key] public int Id [ForeignKey("Folder")] public int FolderId {get; set;} public virtual Folder Folder {get; set;} } I have 2 dbsets in my DbContext: DbSet<Folder> DbSet<Letter> My question is what happens when I add a new Letter? If I later on fetch the folder I added the letters, will those letters be contained in the folder's letters list?

问题 I have this generic CRUD (Controller, Repository, Service, Specification) with multiple entities that use @OneToMany annotations. The project only starts when I comment on these annotations, otherwise I get an error that always indicates a different "DAO" file. Struchture: oga-servicio-principal -src/main/java --com.oga.springboot ---app.principal ----controllers ----crud (My Generic CRUD files) -----controllers -----models ------dao ------dto ------entity ------service ------specifications -

问题 Given the following code public class Course { @Id @GeneratedValue private Long id; private String name; @OneToMany(cascade = CascadeType.ALL, orphanRemoval = true) private List<Review> reviews = new ArrayList<>(); } public class Review { @Id @GeneratedValue private Long id; @Column(nullable = false) private String rating; private String description; } Saved course with 2 reviews. If I try to remove one review from course. course.getReviews().remove(0); Hibernate fires following queries.

问题 This question already has answers here : Select values that meet different conditions on different rows? (6 answers) Closed 2 years ago . A MySQL database contains two tables with a one-to-many relationship: One user can have many settings: Users: id username password -------------------------- 1 Bob 123 2 Alice abc ... Settings: id user_id key value ----------------------------- 1 1 color blue // Bobs settings... 2 1 theme xy 3 1 size 5 4 2 size 5 // Alices settings... Problem: How to find

问题 I have an hypothetical database as the image below were each plant can have a maximum of 4 colours. I wish to be able to return my results in a format similar to the below. If I run a standard query with Inner Join the results are duplicated were the plant has more than one colour. I have therefore tried running multiple separate queries were I first return the plant then a new query to return the colours. I then loop though colour result to produce the output I desire. I assume there is a

问题 How to set the column name of the foreign key when setting up a one-to-many relationship in JPA? I would like to change the name of "items_id" to "item_id" @OneToMany private List<Item> items; I tried the following annotations with no success: @JoinColumn(name="item_id") // join table is not created @Column(name="item_id") // no effect 回答1: You want to override the mappings of the default values of the join table, so the @JoinTable annotation is the one to use. You want to override the name