What is wrong with my relationships in SQL Alchemy?

Question

I am using SQLAlchemy with Flask to create relationships for my application. I recently rewrote the relationships, and, no matter what I change, I keep getting the error: ``` sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship CurriculumVersion.enrollments - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression. ``` On my models: ``` class User(db.Model, AuthUser): id = db.Column(db.Integer, primary_key=True) tf_login = db.Column(db.String(255), unique=True, nullable=False) # can assume is an email password = db.Column(db.String(120), nullable=False) salt = db.Column(db.String(80)) role = db.Column(db.String(80)) # for later when have different permission types zoho_contactid = db.Column(db.String(20), unique=True, nullable=False) created_asof = db.Column(db.DateTime, default=datetime.datetime.utcnow) en…

Accepted Answer

This error:

```
Could not determine join condition between parent/child tables on relationship CurriculumVersion.enrollments 
```

means that SQLAlchemy could not find a proper column in `Enrollments` to use as the foreign key in the relationship.

You defined the foreign key, but you used an incorrect table name. Flask-SQLAlchemy converts `CamelCase` classes to `camel_case` when creating the table, so you need to change this:

```
class Enrollment(db.Model, AuthUser):
    # ...
    version_id = db.Column(db.Integer, db.ForeignKey('curriculumversion.id'))
    #...
```

to this:

```
class Enrollment(db.Model, AuthUser):
    # ...
    version_id = db.Column(db.Integer, db.ForeignKey('curriculum_version.id'))
    #...
```

Alternatively you can use the `__tablename__` attribute to override the default naming convention used by Flask-SQLAlchemy.

What is wrong with my relationships in SQL Alchemy?

Solution

Problem