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How to set check constraint in sql model? #292
Description
First Check
- I added a very descriptive title to this issue.
- I used the GitHub search to find a similar issue and didn't find it.
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- I already checked if it is not related to SQLModel but to SQLAlchemy.
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Example Code
passDescription
SQLAlchemy allows to implement CheckContraint on either column or table level. How can I archive the same in SQLModel, e.g. limiting the possible values of a column to the colors red and green or to ensure that the values within a column are greater than 10.
I suppose it must be somehow possible using sa_column_kwargs (similar to implementing UniqueConstraint).
Help would be highly appreciated, thanks!
Operating System
Windows
Operating System Details
No response
SQLModel Version
0.0.6
Python Version
3.8.1
Additional Context
No response
Activity
jd-solanki commented on Apr 5, 2022
You can use various sa_column* args like:
jd-solanki commented on Apr 5, 2022
I use sa_column for Enum like below:
dannyrohde commented on Apr 21, 2022
One caveat to using columns is that you might need to move properties like index or nullable into the Column description. I found that it otherwise doesn't get honoured.
E.g. the example in the above comment will work, but the below won't have the intended effect:
access_status: EnumAccessStatus = Field( sa_column=Column(SaEnumAccessStatus,), nullable=False, index=True)
LumaC0 commented on Oct 10, 2024
How about CheckConstraint at the table level? I've been setting it in table_args like I'd do in sqlalchemy and just noticed Alembic isn't recognizing it.
YuriiMotov commented on Aug 11, 2025
In current version, you will get a runtime error if you try using nullable or index with sa_column:
Considering this comment from Sebastian
I think that sa_column is the only way to go..
smiling-watermelon commented on Feb 26, 2026
I know that that's pretty tangential to the question at hand, but, has anyone else encountered a problem where by setting sa_column after you've had a field defined without sa_column, when making a migration with alembic, sqlalchemy will raise an exception saying something like:
sqlalchemy.exc.ArgumentError: Column object 'amount' already assigned to Table 'balance'
I've encountered this error while setting CheckConstraint, so, it's sort of related to the question posted here, but not really 😅
UPD: This is related to the inheritance. I suppose table is set on Column and consequently - Field on definition, so, if you have a base model (like I had for balance), you'll have to duplicate the field in your child models 😢
📝 Add documentation for unique and check constraints