android - 如何在房间数据库中添加主键?
问题描述
我有一个 sqlite 数据库,我想将我的数据库更改为Room database
.
其中一张表没有任何主键,只有两个外键。
我用这个查询在房间前创建了表:
CREATE TABLE student_performance(
class_id int ,
student_id char(10),
class_date date ,
absent boolean DEFAULT 0,
delay boolean DEFAULT 0,
positive int DEFAULT 0,
negative int DEFAULT 0,
quiz float ,
FOREIGN KEY (student_id , class_id) REFERENCES student(student_id , class_id)
ON DELETE CASCADE
ON UPDATE CASCADE);
现在我为房间定义表:
@Entity(tableName = "performance",
foreignKeys = {@ForeignKey(
entity = StudentEntry.class,
parentColumns = {CLASS_ID, STUDENT_ID},
childColumns = {CLASS_ID, STUDENT_ID},
onDelete = CASCADE, onUpdate = CASCADE)})
public class PerformanceEntry {
.
.
.
}
但它给出了错误:
error: An entity must have at least 1 field annotated with @PrimaryKey
我不知道如何为房间数据库定义这个表。
解决方案
当存在注释时,不必运行CREATE TABLE
SQL 。添加一个主键(因为几乎是唯一的):tableName
@ColumnInfo
entry_id
class_id
@Entity(
tableName = "performance",
foreignKeys = {
@ForeignKey(
entity = StudentEntry.class,
parentColumns = {CLASS_ID, STUDENT_ID},
childColumns = {CLASS_ID, STUDENT_ID},
onDelete = CASCADE,
onUpdate = CASCADE
)
}
)
public class PerformanceEntry {
/* Fields */
@ColumnInfo(name = "entry_id")
@PrimaryKey(autoGenerate = true)
private int entryId;
...
}