通过可更新视图从 INSERTED 记录返回列

Question

我有一个视图需要允许我的用户更新和插入。重要的是，当他们插入时，他们需要能够 return Inserted 行中的新值，但是现在他们得到 NULL。它必须是一个视图，因为在视图的 SELECT 中，它需要能够 return 作为联接结果的值。

我的基本 table 定义：

CREATE TABLE my_assets (
    asset_id bigserial not null primary key,
    asset_price NUMERIC(32,10) -- This will vary constantly via an independent process
);

CREATE TABLE my_transactions (
    id bigserial not null primary key,
    asset_id bigint not null REFERENCES my_assets(asset_id),
    some_text varchar(100)
);
INSERT INTO my_assets(asset_price) SELECT 100 as asset_price;

我的视图显示 table 的结果：

CREATE VIEW my_transactions_view AS
SELECT tx.id, tx.asset_id, tx.some_text, a.asset_price
FROM my_transactions tx
JOIN my_assets a ON tx.asset_id = a.asset_id

我的触发器允许插入 my_transactions_view:

CREATE OR REPLACE FUNCTION trigfx_insert_to_my_transactions_view()
RETURNS trigger AS
    $BODY$
BEGIN
    INSERT INTO my_transactions(asset_id, some_text)
    SELECT NEW.asset_id, NEW.some_text;
    RETURN NEW;
END
    $BODY$
    LANGUAGE 'plpgsql';

CREATE TRIGGER trig_my_transactions_view INSTEAD OF INSERT on my_transactions_view
FOR EACH ROW EXECUTE PROCEDURE trigfx_insert_to_my_transactions_view();

到目前为止一切都很好。但是，问题出在尝试运行以下 SQL:

INSERT INTO my_transactions_view(asset_id, some_text)
    SELECT 1 as asset_id, 'Hello World' as some_text
    RETURNING id, asset_id, some_text;

returned tablereturns NULL for ID,但我想return新更新的ID来自 my_transactions table:

|---------------------|------------------|------------------|
|         ID          |     asset_id     |    some_text     |
|---------------------|------------------|------------------|
|        null         |         1        |  Hello World     |
|---------------------|------------------|------------------|

运行随后的 SELECT * FROM my_transactions_view 确实会产生更新的结果：

|------------------|------------------|------------------|------------------|
|         ID       |     asset_id     |    some_text     |    asset_price   |
|------------------|------------------|------------------|------------------|
|         1        |         1        |  Hello World     |  100.0000000     |
|------------------|------------------|------------------|------------------|

但我需要它在 INSERT 语句的 RETURNING 期间生成。

谢谢！！！

Answer 1

您可以使用生成的 ID 填充 new 记录：

CREATE OR REPLACE FUNCTION trigfx_insert_to_my_transactions_view()
RETURNS trigger AS
    $BODY$
BEGIN
    INSERT INTO my_transactions(asset_id, some_text)
    values (NEW.asset_id, NEW.some_text);
    new.id := lastval(); --<< this gets the generated id from the transactions table
    RETURN NEW;
END
$BODY$
LANGUAGE plpgsql;

Online example

或者您可以使用 currval(pg_get_serial_sequence('my_transactions','id')) 而不是 lastval()

Answer 2

原来我们可以通过 SELECT INTO 从 CTE 中避免额外的函数调用：

CREATE OR REPLACE FUNCTION trigfx_insert_to_my_transactions_view()
RETURNS trigger AS
    $BODY$
BEGIN
    WITH ins_q as (INSERT INTO my_transactions(asset_id, some_text)
    values (NEW.asset_id, NEW.some_text)
    RETURNING id, asset_id, some_text)
    SELECT ins_q.id, ins_q.asset_id, ins_q.some_text
    INTO NEW.id, NEW.asset_id, NEW.some_text
    FROM ins_q;
    RETURN NEW;
END
$BODY$
LANGUAGE plpgsql;

See online example here. 我运行使用 new.id := lastval(); 方法遇到初始化错误 (lastval is not yet defined in this session)。

通过可更新视图从 INSERTED 记录返回列

Returning a column from an INSERTED record via an updateable view

sql

postgresql

plpgsql

sql-view

database-trigger