如何在“ json_array”类型的列上使用Doctrine在Symfony 3中添加复合索引？

Question

I have a table and I want to add indexes like this:

 @Index(columns={"child_id", "abilities"}),
 @Index(columns={"parent_id", "abilities"}),

...

 * @ORM\Column(type="json_array", length=256)
 */
protected $abilities;

However, even after adding the appropriate limits in the migration:

$this->addSql('CREATE INDEX IDX_1088BF61DD62C21BB8388DA4 ON xxx (child_id, abilities(512))');
$this->addSql('CREATE INDEX IDX_1088BF61727ACA70B8388DA4 ON xxx (parent_id, abilities(512))');

Errors like this occur when running tests, which recreate the database:

An exception occurred while executing '

CREATE TABLE xxx (
    id INT AUTO_INCREMENT NOT NULL, 
    parent_id INT DEFAULT NULL, 
    child_id INT DEFAULT NULL, 
    type VARCHAR(125) NOT NULL, 
    abilities LONGTEXT NOT NULL COMMENT '(DC2Type:json_array)', 
    created_at DATETIME NOT NULL, 
    modified_at DATETIME NOT NULL, 
    INDEX IDX_1088BF61727ACA70 (parent_id), 
    INDEX IDX_1088BF61DD62C21B (child_id), 
    INDEX IDX_1088BF61DD62C21B8CDE5729 (child_id, type), 
    INDEX IDX_1088BF61727ACA708CDE5729 (parent_id, type), 
    INDEX IDX_1088BF618CDE5729 (type), 
    INDEX IDX_1088BF61DD62C21BB8388DA4 (child_id, abilities), 
    INDEX IDX_1088BF61727ACA7 0B8388DA4 (parent_id, abilities), 
    INDEX IDX_1088BF61B8388DA4 (abilities), 
    UNIQUE INDEX UNIQ_1088BF61727ACA70DD62C21B (parent_id, child_id), 
    PRIMARY KEY(id)
) DEFAULT CHARACTER SET utf8 COLLATE utf8_unicode_ci ENGINE = InnoDB

':

SQLSTATE[42000]: Syntax error or access violation: 1170 BLOB/TEXT column 'abilities' used in key specification without a key length

What do I need to do to successfully create indexes on these columns?

Answer 1

There are limitations on indexing long strings.

Since the string in question contains "json", it is useless to have a regular index on that column.

Solution: Get rid of these 3 indexes:

INDEX IDX_1088BF61DD62C21BB8388DA4 (child_id, abilities), 
INDEX IDX_1088BF61727ACA7 0B8388DA4 (parent_id, abilities), 
INDEX IDX_1088BF61B8388DA4 (abilities),