Question

我拥有实体类Person，并且表中的name和feature不应超过一个人。但是，如果我将人员的姓名或特征设置为null，则无法使用。如何使其与空值一起使用？参见下面的代码。

测试

Context context = InstrumentationRegistry.getContext();
AppDb db = Room.inMemoryDatabaseBuilder(context, AppDb.class).allowMainThreadQueries().build();
PersonDao dao = db.personDao();

// replacement works here
dao.insert(new Person("Musk", "Alien"));
dao.insert(new Person("Musk", "Alien"));

// replacement doesn't work here
dao.insert(new Person("Trump", null));
dao.insert(new Person("Trump", null));

// fails - actual size = 3 (Musk, Trump, Trump)
assertEquals(2, dao.getAll().size());

Person.java

import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.Index;
import androidx.room.PrimaryKey;

@Entity(tableName = "person", indices = {@Index(value = {"name", "feature"}, unique = true)})
public class Person {

    @ColumnInfo(name = "id") @PrimaryKey(autoGenerate = true) private int id;
    @ColumnInfo(name = "name") private String name;
    @ColumnInfo(name = "feature") private String feature;

    public Person(String name, String feature) {
        this.name = name;
        this.feature = feature;
    }
    public void setId(int id) { this.id = id; }
    public int getId() { return id; }
    public String getName() { return name; }
    public String getFeature() { return feature; }
}

PersonDao.java

import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;
import java.util.List;

@Dao
public interface PersonDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insert(Person person);

    @Query("SELECT * FROM person")
    List<Person> getAll();

    @Query("SELECT * FROM person WHERE feature = :feature")
    List<Person> getByFeature(String feature);

}

AppDb.java

import androidx.room.Database;
import androidx.room.RoomDatabase;

@Database(
        version = 1,
        exportSchema = false,
        entities = {Person.class}
)
public abstract class AppDb extends RoomDatabase {

    public abstract PersonDao personDao();
}

Answer 1

A null value is unique from any other null value，这就是为什么没有发生UNIQUE约束冲突而必须进行替换的原因。

您可以将feature字段设置为@NonNull，以使null不是有效值，如果为空，则可以使用默认值/魔术值，例如"NONE"。

或者，如果您不真正使用id，则可以将其删除，并将PRIMARY KEY更改为name字段，例如，将Person插入相同名称但不同的功能将被替换。

具有空值的实体的会议室（SQLite）替换策略不起作用

1 个答案: