AFTER INSERT OR UPDATE 触发器违反非空常量答案

【问题标题】：AFTER INSERT OR UPDATE trigger violates not-null constantAFTER INSERT OR UPDATE 触发器违反非空常量
【发布时间】：2016-02-19 12:40:52
【问题描述】：

在文字游戏 SQLite 数据库中，我想以明文存储简短的单词和带有很少Q 字母的单词（以便能够在应用程序中列出它们）。

否则我只想存储一个单词的 MD5 哈希值（这样应用程序数据库就不会被轻易窃取）。

在后端我使用 PostgreSQL 9.5 并准备了存储函数：

CREATE OR REPLACE FUNCTION hash_word(in_word varchar(255))
        RETURNS varchar(32) AS
$func$
        SELECT CASE WHEN LENGTH(in_word) > 3 AND in_word !~ 'Q'
        THEN UPPER(MD5(in_word)) ELSE in_word END
$func$ LANGUAGE sql IMMUTABLE;

这似乎工作正常：

# SELECT hash_word('ABC');
 hash_word
-----------
 ABC
(1 row)

# SELECT hash_word('ABCDE');
            hash_word
----------------------------------
 2ECDDE3959051D913F61B14579EA136D
(1 row)

# SELECT hash_word('SQUAD');
 hash_word
-----------
 SQUAD
(1 row)

然后我创建一个表来存储大写英文单词及其散列值和 INSERT OR UPDATE 触发器：

CREATE OR REPLACE FUNCTION english_nouns_trigger()
        RETURNS TRIGGER AS
$func$
BEGIN
        DELETE FROM english_nouns WHERE word = NEW.word;

        INSERT INTO english_nouns(word, hashed)
        VALUES (NEW.word, hash_word(new.word));

        RETURN NEW;
END
$func$ LANGUAGE plpgsql;

DROP table IF EXISTS english_nouns;
CREATE TABLE english_nouns (
        word varchar(255) PRIMARY KEY CHECK (word ~ '^[A-Z]{2,}$' AND
                word !~ 'JQ' AND
                word !~ 'QG' AND
                word !~ 'QK' AND
                word !~ 'QY' AND -- impossible english bigrams
                word !~ 'QZ' AND
                word !~ 'WQ' AND
                word !~ 'WZ'),
        hashed varchar(32) NOT NULL
);

CREATE TRIGGER english_nouns_trigger
AFTER INSERT OR UPDATE ON english_nouns
FOR EACH ROW EXECUTE PROCEDURE english_nouns_trigger();

不幸的是，当我尝试插入测试值时，我得到了错误：

# INSERT INTO english_nouns (word) VALUES ('ABC'), ('ABCDE'), ('SQUAD');

ERROR:  null value in column "hashed" violates not-null constraint
DETAIL:  Failing row contains (ABC, null).

更新：

当我按照 Richard 的建议将 AFTER 更改为 BEFORE 时（谢谢！）-

CREATE TRIGGER english_nouns_trigger
BEFORE INSERT OR UPDATE ON english_nouns
FOR EACH ROW EXECUTE PROCEDURE english_nouns_trigger();

然后我不幸又遇到了另一个错误：

# INSERT INTO english_nouns (word) VALUES ('ABC'), ('ABCDE'), ('QI');

ERROR:  stack depth limit exceeded
HINT:  Increase the configuration parameter "max_stack_depth" (currently 2048kB), after ensuring the platform's stack depth limit is adequate.
CONTEXT:  SQL statement "DELETE FROM english_nouns
        WHERE word = NEW.word"
PL/pgSQL function english_nouns_trigger() line 3 at SQL statement
SQL statement "INSERT INTO english_nouns(word, hashed) 
        VALUES (NEW.word, hash_word(new.word))"
PL/pgSQL function english_nouns_trigger() line 6 at SQL statement
SQL statement "INSERT INTO english_nouns(word, hashed) 
        VALUES (NEW.word, hash_word(new.word))"

【问题讨论】：

标签： postgresql stored-procedures triggers sql-insert postgresql-9.5

【解决方案1】：

您想在插入数据之前更改数据吗？使用前触发器，而不是后触发器。

【讨论】：

【解决方案2】：

您的表格中有 2 行：

word varchar(255) 
hashed varchar(32) NOT NULL

您只是为 word 插入一个值。所以基本上你真正插入的是：

INSERT INTO english_nouns (word, hashed) VALUES ('ABC', NULL), ('ABCDE', NULL), ('SQUAD', NULL);

不为散列值插入带有 NOT NULL 限制的值会引发该错误。

您需要为散列值插入一些值：

INSERT INTO english_nouns (word, hashed) VALUES ('ABC', somevalue), ('ABCDE', somevalue), ('SQUAD', somevalue);

【讨论】：

【解决方案3】：

好的，下面的BEFORE 触发器似乎可以工作：

CREATE OR REPLACE FUNCTION hash_word(in_word varchar(255))
        RETURNS varchar(32) AS
$func$
        SELECT CASE WHEN LENGTH(in_word) > 3 AND in_word !~ 'Q' 
        THEN UPPER( MD5(in_word) ) ELSE in_word END
$func$ LANGUAGE sql IMMUTABLE;


CREATE OR REPLACE FUNCTION english_nouns_trigger()
        RETURNS TRIGGER AS
$func$
BEGIN
        NEW.hashed := hash_word(NEW.word);

        RETURN NEW;
END
$func$ LANGUAGE plpgsql;


DROP table IF EXISTS english_nouns;
CREATE TABLE english_nouns (
        word varchar(255) PRIMARY KEY CHECK (word ~ '^[A-Z]{2,}$' AND
                word !~ 'JQ' AND 
                word !~ 'QG' AND 
                word !~ 'QK' AND 
                word !~ 'QY' AND 
                word !~ 'QZ' AND 
                word !~ 'WQ' AND 
                word !~ 'WZ'),
        hashed varchar(32) NOT NULL
);

CREATE TRIGGER english_nouns_trigger 
BEFORE INSERT OR UPDATE ON english_nouns
FOR EACH ROW EXECUTE PROCEDURE english_nouns_trigger();

演示INSERT：

# INSERT INTO english_nouns (word) VALUES ('ABC'), ('ABCDE'), ('QI');
INSERT 0 3

# TABLE english_nouns;
 word  |              hashed              
-------+----------------------------------
 ABC   | ABC
 ABCDE | 2ECDDE3959051D913F61B14579EA136D
 QI    | QI
(3 rows)

演示UPDATE：

# UPDATE english_nouns SET word = 'ABCDEF' WHERE word = 'ABCDE';
UPDATE 1

# TABLE english_nouns;
  word  |              hashed              
--------+----------------------------------
 ABC    | ABC
 QI     | QI
 ABCDEF | 8827A41122A5028B9808C7BF84B9FCF6
(3 rows)

【讨论】：