android – Room Composite主键的外键

2019-07-05 15:23:31 阅读：1075 来源： 互联网

标签：android sqlite foreign-keys primary-key android-room

我正在使用Room数据库实现一个Android应用程序,并且对这个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;

}

两个表’Food’和’Ingredient’都有复合主键(‘id’,’language_id’). 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 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).

有人可以帮助我吗？

提前致谢：)

解决方法:

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)

区别在于我在’parentColumns’和’childColumns’中放置了多个列,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),之后是关系中的每个数据

标签：android,sqlite,foreign-keys,primary-key,android-room
来源： https://codeday.me/bug/20190705/1388641.html

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android – Room Composite主键的外键