我正在使用 Room 数据库实现一个 android 应用程序，并且有一个关于这个数据库中的关系的小问题。

我有两个表:

@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;

}

'Food' 和 'Ingredient' 这两个表都有复合主键('id'，'language_id')。 Food 对象必须包含一个列表，当然还有一个@Relationship

public class FoodWithIngredients extends Food{

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

}

在我尝试运行此代码后收到这些消息

警告:

food_language_id column references a foreign key but it is not part of an index. This may trigger full table scans whenever parent table is modified so you are highly advised to create an index that covers this column.

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:)

最佳答案

好的，我发现我错在哪里了。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”中放置了多个列，它工作正常。

@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)，然后是关系中的每个数据

关于android - 房间复合主键链接到外键，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/50248668/