The Boolean property write to mysql and then read out can not serialize problem

[tingruizhang]

my model entity contains an boolean property like

deleted = db.Column(db.Boolean, default=False)

after a model entity write to mysql, mysql schema the according delete column type is tinyint, so the property 'deleted' in mysql is 0 or 1.

while I read the value of my entity from mysql, the property 'deleted' can not serialized.

I want to learn more from you. thanks.

[tingruizhang]

Is there any methods can resolve this?

[n0nSmoker]

Hi, please share more details. What error you are getting?

[n0nSmoker]

MySQL stores db.Boolean as TINYINT (0/1), and SQLAlchemy may return it as an int instead of a bool. The serializer only handles actual bool values, so integers pass through unchanged.

Use serialize_columns to convert the integer to a boolean.

Solution 1: Per-instance (recommended for quick fixes)

Convert integer (0/1) to boolean

result = model.to_dict(
    serialize_columns={        
       'deleted': lambda v: bool(v) if isinstance(v, int) else v
    }
)

Solution 2: Class-level (for all instances)

class YourModel(db.Model, SerializerMixin):    
    deleted = db.Column(db.Boolean, default=False)        
    serialize_columns = {
        'deleted': lambda v: bool(v) if isinstance(v, (int, bool)) else v    
    }

Solution 3: Automatic detection (if you have multiple boolean columns)

class YourModel(db.Model, SerializerMixin):
    deleted = db.Column(db.Boolean, default=False)    
    active = db.Column(db.Boolean, default=True)
    serialize_columns = {
        'deleted': lambda v: bool(v) if v in (0, 1) else v,
        'active': lambda v: bool(v) if v in (0, 1) else v,
    }

Why this works:
serialize_columns applies a custom serializer to specific columns before normal serialization.
The lambda converts int (0/1) to bool (False/True).
The serializer then handles the bool value correctly.