one-to-many

问题 There are two main @Entity classes reflecting these tables: TableA {id,name} TableB {id,name} And one reference table TableC {tableA.id,tableB.id} Question is: how to map a TableA 's entity's field with @OneToMany realation to TableB objects list: @OneToMany ?????????? private List<TableBEntity> tableBItems; 回答1: If what you really have is a OneToMany (which means that a give tableB.id appears at most once in TableC ), then the mapping is the following: @OneToMany @JoinTable(name = "TableC",

问题 User have n Contacts. A Contact can have a localized Comment (Comments are shared between Contacts). Java Beans: @Audited @Entity public class User { @OneToMany(fetch = FetchType.EAGER, cascade = CascadeType.ALL, orphanRemoval = true) Set<Context> contacts; } @Audited @Entity public class Contact { @ManyToOne(fetch = FetchType.EAGER, cascade = { CascadeType.MERGE, CascadeType.PERSIST, CascadeType.REFRESH}) Comment comment; } @Audited @Entity public class Comment { String de; String en; String

问题 I am trying to develop spring rest api with hibernate. after searching in google, I have not find solution to lazy loading. I have two entity like below: University.java @Entity() @Table(schema = "core", name = "university") public class University extends BaseEntity { private String uniName; private String uniTelephon; @LazyCollection(LazyCollectionOption.FALSE) @OneToMany(fetch = FetchType.LAZY, mappedBy = "university", cascade = CascadeType.ALL) @JsonManagedReference private List<Student>

问题 Say I have a couple objects, having a one-to-many relationship, something like class Parent(): //id, other cols, etc children = relationship("Child", backref="parent") class Child(): parent_id = Column(Integer, ForeignKey("parent.id") child_type = Column(Enum("a","b")) Now, I want to query Parent objects, but have their children filtered by child_type, ie something like session.query(Parent).join(Parent.children).filter(Child.child_type == "a") This just returns the Parent with all the

问题 Let's say I have the following situation: Object Car has an ArrayList of prices, which are all numbers. Is it possible in Hibernate to save all the prices in a single column? I know this violates the first normal form but there might be cases when you don't want them to be saved in a separate table like it's classically done in One-To-Many or Many-To-Many relationships. In JDO I'd do this easily by saving the ArrayList in a BLOB column. Some useful related SOF questions: ArrayList of

问题 I am new to Hibernate. I notice that in Hibernate, mapping the java classes into database tables often involve relation tables, even sometimes relation tables are not necessary(Like in a one-to-many relation or the opposite). For example: I am a Company class and a Flight class, in which a company can have many flights(a one to many association from Company to Flight). I have the following code using hibernate annotations: @Entity @Table(name = "COMPANY") public class Company { @Id private

问题 I am at the moment creating a complicated rails form for 1:n relationship with nested form and collection select with values from yet another data table. So far, it overwrites the database value with the first entry in the values list of the collection_select whenever the user does not select the correct value before update. I still need to set the initial value in the collection_select correctly. I have read a lot of questions on SO already, most relevant was: f-collection-select-not

问题 I am creating a photo sharing app for the iPhone using Parse.com and so far everything has been pretty easy and I just finished writing the code for uploading photos to the Parse server. So far, I have been using the default "_User" class. Here are some of the key types of data that are being stored for each user: objectId, username, email, and an array object called "friends" that contains the usernames of other users in the database that the user has added to their friends list. Now, I need

问题 This is a syntax question. I want a one-to-many relationship between Foo -> Bar (simplified here): class Foo { String fooPK1, fooPK2 static mapping = { id composite: ["fooPK1", "fooPK2"] } static hasMany = [bars: Bar] } class Bar { String fooPK1, dumbNameForFooPK2, barPK1, barPK2 Foo myFoo static mapping = { id composite: ["barPK1", "barPK2"] columns { myFoo[:] { column name: "FOO_PK_1" column name: "?????????????" } } } } In this case, obviously Foo.fooPK1 maps to Bar.fooPK1, but i need Foo

问题 I am trying to create a entity as follows @Data public class Person { @Id private String id; @OneToMany(mappedBy="id") private List<person> friends; } Letting JPA create entity and i am able to persist person with friends as null when trying to save a new person with friends list populated , the relation is not visible in RDBMS and its not throwing any error while saving. Not able to figure out is the friend data actually getting stored ? If yes , how to access it ? 回答1: Assuming you have two