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Unexpected differing behavior for db.String and db.Text on Postgres (latter saves empty field as "") #1840

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boydgreenfield opened this issue Apr 4, 2019 · 1 comment · Fixed by #2321
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Unexpected differing behavior for db.String and db.Text on Postgres (latter saves empty field as "") #1840

boydgreenfield opened this issue Apr 4, 2019 · 1 comment · Fixed by #2321

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@boydgreenfield
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boydgreenfield commented Apr 4, 2019 •
edited

This seems related to a bunch of closed issues around handling nullable and non-nullable fields, but I recently was stumped by the following (IMO) weird behavior:

from app import admin, db  # vanilla Flask setup
from flask_admin.contrib.sqla import ModelView

# Declarative model using Flask-SQLAlchemy, Postgres as the backend
class Document(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    description = db.Column(db.String)

class Document2(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    description = db.Column(db.Text)

### Add to Flask-Admin instance
admin.add_view(ModelView(Document, db.session))

Leads to Document instances having a null description field when they're created in Flask-Admin (what I'd expect by default) and Document2 instances having an empty string. In Postgres, I believe these are actually equivalent, so I can just use db.String as a workaround.

Is this a bug? Edge case of something about these column types I'm not thinking of (or that doesn;'t apply to Postgres)? Certainly a bit of a gotcha that I didn't jump out at me in any of the documentation or examples.
@b-ryan
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b-ryan commented Jun 17, 2019

I ran into this as well. I tracked it down to the difference between these two functions:

https://github.com/flask-admin/flask-admin/blob/d29796b6998b9fc86fbf0acc08aba0b27edbd013/flask_admin/contrib/sqla/form.py#L274-L301

The text converter doesn't do any work to check if the column is nullable and this is, I believe, the root of the issue.

I came up with the following to get around this

class MyModelConverter(sqla.form.AdminModelConverter):

    real_text_columns = [
        # any columns that should be treated like textarea fields should be listed here
    ]

    @converts("Text")
    def conv_Text(self, field_args, **extra):
        if extra["column"] in self.real_text_columns:
            return super().conv_Text(field_args, **extra)
        column = extra.pop("column")
        return self.conv_String(column, field_args, **extra)

There's certainly issues with this, like that you have to explicitly list out the "real" text columns. And I don't know what the implications of @converts("Text") are. However, it's working for my own purposes.

@ElLorans ElLorans mentioned this issue Sep 28, 2022
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@dgilman dgilman mentioned this issue Jan 19, 2023
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String null fix dgilman/flask-admin
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@boydgreenfield @b-ryan