[RUBY] [Rails] Let's dynamically get the threshold of model validation "length check" from table information

Suppose you have the following users table.

mysql> desc users;
| Field                       | Type        | Null | Key | Default | Extra          |
| id                          | bigint(20)  | NO   | PRI | NULL    | auto_increment |
| name                        | varchar(100)| NO   |     | NULL    |                |
| created_at                  | datetime    | NO   |     | NULL    |                |
| updated_at                  | datetime    | NO   |     | NULL    |                |

In this case, when creating a Rails User model, I think that name is often validated with less than 100 characters. At that time, did you hard-code 100 as shown below?


validates :name, presence: true, length: { maximum: 100 }

Rails makes it easy to get meta information about database tables. By using this, 100 parts can be dynamically taken from the table definition as shown below.

validates :name, presence: true, length: { maximum: columns.find{|c| c.name == 'name' }.limit }

It is recommended to write like this because the validation value will be updated automatically when the table definition is changed.

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