获取在具有相同列 ID 的房间中连接两个 table 的数据

Question

您好，我正在使用两个 table 学生和 student_address，在这两个 table（在任何情况下都无法更改）

我正在使用 class StudentAndAddress 作为

public class StudentAndAddress{

    @Embedded
    private Student student;

    @Embedded(prefix = "type_")
    private StudentAddress studentAddress;

    public Address getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }

    public StudentAddress getStudentAddress() {
        return studentAddress;
    }

    public void setStudentAddress(StudentAddress studentAddress) {
        this.studentAddress = studentAddress;
    }

}

我正在使用的查询：

@Query("SELECT * FROM student  INNER JOIN student_address ON student.uid == student_address.address_uid and address_link.linkto_type==:linkToType")
LiveData<List<StudentAndAddress>> getStudentAndAddress(String linkToType);

我正在获取第一个 table 的值，但没有获取第二个 table 的值。在数据库中 table 都在那里

Answer 1

我认为，问题的根源是您给@Embedded 的前缀：

@Embedded(prefix = "type_")
private StudentAddress studentAddress;

那个房间无法匹配查询结果中的字段名称和 class StudentAndAddress 中的字段。您必须摆脱前缀（然后 filelds 的名称将相等）或更改地址查询中的别名 table（将您的前缀添加到它们中）- 像这样：

@Query("SELECT student.*,addresses.[field1] as type_[field1], adsresses.address_uid as type_address_uid, ... FROM student  INNER JOIN student_address as addresses ..."

Answer 2

在 room 中，我们需要使用关系解决此类查询

public class StudentAndAddress{

    @Embedded
    private StudentAddress studentAddress;


    @Relation(
            parentColumn = "address_uid",
            entityColumn = "uid",
            entity = Student.class
    )
    private Student student;


    public Address getStudent() {
        return student;
    }

    public void setStudent(Student student) {
        this.student = student;
    }

    public StudentAddress getStudentAddress() {
        return studentAddress;
    }

    public void setStudentAddress(StudentAddress studentAddress) {
        this.studentAddress = studentAddress;
    }

}

我们需要写的查询是：-

@Query("SELECT * FROM student_address WHERE linkto_type==:linkToType")
LiveData<List<StudentAndAddress>> getStudentAndAddress(String linkToType);

获取在具有相同列 ID 的房间中连接两个 table 的数据

Get data joining two table in room having same column id

orm

android

android-sqlite

spring-boot

android-room