You are referencing the wrong type in the documentation. In your code, you have type="string" , but your link to the documentation is related to type="object" .
If you read the part of the table above in the referenced documents, you will see that string converted to VARCHAR in MySQL if length does not exceed the maximum length for MySQL, and converted to MEDIUMTEXT if length exceeds.
But if you want to get an explicit TEXT field, you need to define your column using type="text" .
Michael Sivolobov
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