Question

我正在使用Room数据库实现一个Android应用程序，并且对此数据库中的关系有一个小问题。

我有两张桌子：

@Entity(tableName = "foods", primaryKeys = {"id", "language_id"},
        indices = {@Index(value = {"id", "language_id"}, unique = true)},
        inheritSuperIndices = true)
public class Food {

    @NonNull
    @ColumnInfo(name = "id")
    private String mId;

    @NonNull
    @ColumnInfo(name = "language_id")
    private String mLanguageId;

}

@Entity(tableName = "ingredients", primaryKeys = {"id", "language_id"},
        indices = {@Index(value = {"id", "language_id"}, unique = true), 
        @Index(value = {"food_id", "food_language_id"}, unique = true)},
        foreignKeys = {@ForeignKey(entity = Food.class, parentColumns ="id", 
        childColumns = "food_id", onUpdate = CASCADE, onDelete = CASCADE),
        @ForeignKey(entity = Food.class, parentColumns = "language_id", 
        childColumns = "food_language_id", onUpdate = CASCADE, onDelete = 
        CASCADE)},
        inheritSuperIndices = true)
public class Ingredient {

    @NonNull
    @ColumnInfo(name = "id")
    private String mId;

    @NonNull
    @ColumnInfo(name = "language_id")
    private String mLanguageId;

    @ColumnInfo(name = "food_id")
    private String mFoodId;

    @ColumnInfo(name = "food_language_id")
    private String mFoodLanguageId;

}

两张桌子＆＃39; Food＆＃39;和＆＃39;成分＆＃39;拥有复合主键（＆＃39; id＆＃39;，＆＃39; language_id＆＃39;）。 Food对象必须包含List，当然还有@Relationship

public class FoodWithIngredients extends Food{

    @Relation(parentColumn = "id", entityColumn = "food_id", entity = 
    Ingredient.class)
    private List<Ingredient> mIngredients;

}

我尝试运行此代码后收到这些消息

WARNNING：

food_language_id列引用了一个外键，但它不属于一个索引。无论父表是什么，这都可能触发全表扫描已修改，因此强烈建议您创建一个涵盖此内容的索引列。

错误：

Ingredient has a foreign key (food_id) that references Food (id) but Food does not have a unique index on those columns nor the columns are its primary key. SQLite requires having a unique constraint on referenced parent columns so you must add a unique index to Food that has (id) column(s).

有人可以帮我吗？

提前致谢：）

Answer 1

好的，我发现我的错误在哪里。我的@ForeignKey错了，正确的是：

@ForeignKey(
             entity = Food.class,
             parentColumns = {"id", "language_id"},
             childColumns = {"food_id", "food_language_id"},
             onUpdate = CASCADE, onDelete = CASCADE)

不同之处在于我在'parentColumns'和'childColumns'中添加了多个列，它的工作正确。

@Danail Alexiev插入是这样的：

@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertFoods(List<Food> foods);

@Insert(onConflict = OnConflictStrategy.REPLACE)
void insertIngredients(List<Ingredient> ingredients);

@Transaction
public void insertFoodData(List<Food> foods, RulesOfGolfDatabase database) {
    if (foods != null && database != null) {
        insertFoods(foods);
        for (Food food : foods) {
            insertIngredients(food.getIngrediants());
        }
    }
}

这里最重要的是你必须首先插入@Relation的所有者（在这个例子中是Food），然后插入关系中的每个数据

房间复合主键链接到外键

1 个答案: