如何在不丢失外键的情况下合并两个sqlite数据库？

Question

我正在开发使用flutter和sqflite软件包学习外语的移动应用程序。该应用程序具有sqlite数据库，其中包含单词表和某种类型的集合（多对多关系）。此数据存储在应用程序资产中，并在安装应用程序时像在sqflite指南https://github.com/tekartik/sqflite/blob/master/sqflite/doc/opening_asset_db.md中一样加载到移动数据库目录中
用户可以添加自己的单词和集合，也可以添加或更改我的单词。我曾经认为我可以使用sqlite upsert来实现，但是如果用户添加的单词与我在应用程序更新中添加的单词相同，则会出现冲突。如果我执行upsert，则该单词不会出现在我的单词集中，因为它们受id约束；否则，如果我执行replace，则单词将从用户的集合中消失。

我认为我需要在sqlite insert or replace中进行某种级联ID更新，但是没有这种功能。

有什么想法吗？

Answer 1

  

我认为我需要在sqlite插入或   替换，但没有这种功能。

有这样的功能；您可以将ON UPDATE CASCADE指定为FOREIGN KEY定义/条款的一部分。您还可以编码ON DELETE CASCADE SQLite Foreign Key Support - 4.3. ON DELETE and ON UPDATE Actions。

由于这被编码为子表的一部分，因此您不能使用ALTER TABLE COLUMN更改列的属性（除了重命名列之外）。您将必须：-

1. 重命名子表。
2. 使用更改后的原始名称创建替换表，然后使用INSERT INTO replacement_table_with_original_name SELECT * FROM renamed_table（显然更改了 replacement_table_with_original_name 和 renamed_table ）为实际名称。
3. 当高兴地放弃重命名的表时。

示例

例如，考虑您的场景的以下表示形式（从可用信息中），然后将在保留现有数据的同时添加ON UPDATE CASCADE和ON DELETE CASCADE，它还会删除没有冲突的行并进行更新没有冲突或损失的参考值：-

-- Create the original tables and load some test data
CREATE TABLE IF NOT EXISTS word_table (id INTEGER PRIMARY KEY, other_column TEXT);
INSERT INTO word_table VALUES (null,'WA'),(null,'WB'),(null,'WC');
CREATE TABLE IF NOT EXISTS collection_table (id INTEGER PRIMARY KEY, other_column TEXT);
INSERT INTO collection_table VALUES (null,'CA'),(null,'CB'),(null,'CC');
CREATE TABLE IF NOT EXISTS word_collection_map (
    word_reference INTEGER NOT NULL REFERENCES word_table(id), 
    collection_reference  INTEGER NOT NULL REFERENCES collection_table(id), 
    PRIMARY KEY (word_reference,collection_reference) ) WITHOUT ROWID;
INSERT INTO word_collection_map VALUES(1,1),(3,2),(3,3),(2,1),(2,2),(2,3);

-- show the result
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
;

-- ADDING CASCADE
ALTER TABLE word_collection_map RENAME TO old_word_collection_map;
CREATE TABLE IF NOT EXISTS word_collection_map (
    word_reference INTEGER NOT NULL REFERENCES word_table(id) ON UPDATE CASCADE ON DELETE CASCADE , 
    collection_reference  INTEGER NOT NULL REFERENCES collection_table(id)  ON UPDATE CASCADE ON DELETE CASCADE, 
    PRIMARY KEY (word_reference,collection_reference) ) WITHOUT ROWID;
INSERT INTO word_collection_map SELECT * FROM old_word_collection_map;
DROP TABLE IF EXISTS old_word_collection_map;
-- Show results (should match first)
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
;

-- DELETE a word no conflicts
DELETE FROM word_table WHERE other_column = 'WC';
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
;

-- UPDATE the FK parent no conflicts
UPDATE collection_table SET id = 10 WHERE id = 3;
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
;

结果：-

日志：-

-- Create the original tables and load some test data
CREATE TABLE IF NOT EXISTS word_table (id INTEGER PRIMARY KEY, other_column TEXT)
> OK
> Time: 0.118s


INSERT INTO word_table VALUES (null,'WA'),(null,'WB'),(null,'WC')
> Affected rows: 3
> Time: 0.104s


CREATE TABLE IF NOT EXISTS collection_table (id INTEGER PRIMARY KEY, other_column TEXT)
> OK
> Time: 0.097s


INSERT INTO collection_table VALUES (null,'CA'),(null,'CB'),(null,'CC')
> Affected rows: 3
> Time: 0.094s


CREATE TABLE IF NOT EXISTS word_collection_map (
    word_reference INTEGER NOT NULL REFERENCES word_table(id), 
    collection_reference  INTEGER NOT NULL REFERENCES collection_table(id), 
    PRIMARY KEY (word_reference,collection_reference) ) WITHOUT ROWID
> OK
> Time: 0.097s


INSERT INTO word_collection_map VALUES(1,1),(3,2),(3,3),(2,1),(2,2),(2,3)
> Affected rows: 6
> Time: 0.105s


-- show the result
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
> OK
> Time: 0.001s


-- ADDING CASCADE
ALTER TABLE word_collection_map RENAME TO old_word_collection_map
> OK
> Time: 0.108s


CREATE TABLE IF NOT EXISTS word_collection_map (
    word_reference INTEGER NOT NULL REFERENCES word_table(id) ON UPDATE CASCADE ON DELETE CASCADE , 
    collection_reference  INTEGER NOT NULL REFERENCES collection_table(id)  ON UPDATE CASCADE ON DELETE CASCADE, 
    PRIMARY KEY (word_reference,collection_reference) ) WITHOUT ROWID
> OK
> Time: 0.096s


INSERT INTO word_collection_map SELECT * FROM old_word_collection_map
> Affected rows: 6
> Time: 0.094s


DROP TABLE IF EXISTS old_word_collection_map
> OK
> Time: 0.081s


-- Show results (should match first)
SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
> OK
> Time: 0s


-- DELETE a word no conflicts
DELETE FROM word_table WHERE other_column = 'WC'
> Affected rows: 1
> Time: 0.086s


SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
> OK
> Time: 0.001s


-- UPDATE the FK parent no conflicts
UPDATE collection_table SET id = 10 WHERE id = 3
> Affected rows: 1
> Time: 0.089s


SELECT word_table.other_column, collection_table.other_column 
FROM word_collection_map 
    JOIN word_table ON word_table.id = word_reference
    JOIN collection_table ON collection_table.id = collection_reference
> OK
> Time: 0s

结果1（基础数据）

结果2（模式更改后）

结果3（删除后）

结果4（更新后）