Question

在单词游戏SQLite数据库中，我想在明文中存储很少Q个字母的简短单词和单词（以便能够在应用程序中列出它们）。< / p>

否则我只想存储一个单词的MD5哈希（以便应用程序数据库不容易被盗）。

在后端，我使用PostgreSQL 9.5并准备了存储的函数：

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的英语单词及其散列值以及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，在尝试插入测试值时，我收到错误：

# 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

当我按照理查德的建议将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();

然后我不幸得到另一个错误：

# 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))"

Answer 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。

Answer 2

表格中有两行：

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

您只是为word插入一个值。所以你真正插入的是：

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

不插入hashed值，并使用NOT NULL限制将引发该错误。

您需要为哈希值插入一些值：

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

Answer 3

好的，以下BEFORE触发似乎有效：

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();

示范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)

示范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)

INSERT INSERT或UPDATE触发器违反非空常量

3 个答案: