Android Room Persistence Library:Upsert [英] Android Room Persistence Library: Upsert

问题描述

Android的Room Persistence库轻松包含了适用于对象或集合的@Insert和@Update批注.但是，我有一个用例(包含模型的推送通知)，由于数据库中可能存在或可能不存在数据，因此需要UPSERT.

Android's Room persistence library graciously includes the @Insert and @Update annotations that work for objects or collections. I however have a use case (push notifications containing a model) that would require an UPSERT as the data may or may not exist in the database.

Sqlite本身没有upsert，并且此 SO问题.鉴于那里的解决方案，人们将如何将其应用于Room?

Sqlite doesn't have upsert natively, and workarounds are described in this SO question. Given the solutions there, how would one apply them to Room?

更具体地说，如何在Room中实现不会破坏任何外键约束的插入或更新?在onConflict = REPLACE上使用insert会导致onDelete调用该行的任何外键.在我的情况下，onDelete导致级联，而重新插入一行将导致其他表中具有外键的行被删除.这不是预期的行为.

To be more specific, how can I implement an insert or update in Room that would not break any foreign key constraints? Using insert with onConflict=REPLACE will cause the onDelete for any foreign key to that row to be called. In my case onDelete causes a cascade, and reinserting a row will cause rows in other tables with the foreign key to be deleted. This is NOT the intended behavior.

推荐答案

也许您可以将BaseDao设置为这样.

Perhaps you can make your BaseDao like this.

通过@Transaction确保upsert操作的安全， 并尝试仅在插入失败时进行更新.

secure the upsert operation with @Transaction, and try to update only if insertion is failed.

@Dao
public abstract class BaseDao<T> {
    /**
    * Insert an object in the database.
    *
     * @param obj the object to be inserted.
     * @return The SQLite row id
     */
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    public abstract long insert(T obj);

    /**
     * Insert an array of objects in the database.
     *
     * @param obj the objects to be inserted.
     * @return The SQLite row ids   
     */
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    public abstract List<Long> insert(List<T> obj);

    /**
     * Update an object from the database.
     *
     * @param obj the object to be updated
     */
    @Update
    public abstract void update(T obj);

    /**
     * Update an array of objects from the database.
     *
     * @param obj the object to be updated
     */
    @Update
    public abstract void update(List<T> obj);

    /**
     * Delete an object from the database
     *
     * @param obj the object to be deleted
     */
    @Delete
    public abstract void delete(T obj);

    @Transaction
    public void upsert(T obj) {
        long id = insert(obj);
        if (id == -1) {
            update(obj);
        }
    }

    @Transaction
    public void upsert(List<T> objList) {
        List<Long> insertResult = insert(objList);
        List<T> updateList = new ArrayList<>();

        for (int i = 0; i < insertResult.size(); i++) {
            if (insertResult.get(i) == -1) {
                updateList.add(objList.get(i));
            }
        }

        if (!updateList.isEmpty()) {
            update(updateList);
        }
    }
}

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