Chapter 12: Database representaton of followers (12a)

app/models.py

@@ -71,6 +71,15 @@ class Role(db.Model):
         return '<Role %r>' % self.name
 
 
+class Follow(db.Model):
+    __tablename__ = 'follows'
+    follower_id = db.Column(db.Integer, db.ForeignKey('users.id'),
+                            primary_key=True)
+    followed_id = db.Column(db.Integer, db.ForeignKey('users.id'),
+                            primary_key=True)
+    timestamp = db.Column(db.DateTime, default=datetime.utcnow)
+
+
 class User(UserMixin, db.Model):
     __tablename__ = 'users'
     id = db.Column(db.Integer, primary_key=True)
@@ -86,6 +95,16 @@ class User(UserMixin, db.Model):
     last_seen = db.Column(db.DateTime(), default=datetime.utcnow)
     avatar_hash = db.Column(db.String(32))
     posts = db.relationship('Post', backref='author', lazy='dynamic')
+    followed = db.relationship('Follow',
+                               foreign_keys=[Follow.follower_id],
+                               backref=db.backref('follower', lazy='joined'),
+                               lazy='dynamic',
+                               cascade='all, delete-orphan')
+    followers = db.relationship('Follow',
+                                foreign_keys=[Follow.followed_id],
+                                backref=db.backref('followed', lazy='joined'),
+                                lazy='dynamic',
+                                cascade='all, delete-orphan')
 
     def __init__(self, **kwargs):
         super(User, self).__init__(**kwargs)
@@ -185,6 +204,28 @@ class User(UserMixin, db.Model):
         return '{url}/{hash}?s={size}&d={default}&r={rating}'.format(
             url=url, hash=hash, size=size, default=default, rating=rating)
 
+    def follow(self, user):
+        if not self.is_following(user):
+            f = Follow(follower=self, followed=user)
+            db.session.add(f)
+
+    def unfollow(self, user):
+        f = self.followed.filter_by(followed_id=user.id).first()
+        if f:
+            db.session.delete(f)
+
+    def is_following(self, user):
+        if user.id is None:
+            return False
+        return self.followed.filter_by(
+            followed_id=user.id).first() is not None
+
+    def is_followed_by(self, user):
+        if user.id is None:
+            return False
+        return self.followers.filter_by(
+            follower_id=user.id).first() is not None
+
     def __repr__(self):
         return '<User %r>' % self.username
 

flasky.py

@@ -1,7 +1,7 @@
 import os
 from flask_migrate import Migrate
 from app import create_app, db
-from app.models import User, Role, Permission, Post
+from app.models import User, Role, Permission, Post, Follow
 
 
 app = create_app(os.getenv('FLASK_CONFIG') or 'default')
@@ -10,7 +10,8 @@ migrate = Migrate(app, db)
 
 @app.shell_context_processor
 def make_shell_context():
-    return dict(db=db, User=User, Role=Role, Permission=Permission, Post=Post)
+    return dict(db=db, User=User, Follow=Follow, Role=Role,
+                Permission=Permission, Post=Post)
 
 
 @app.cli.command()

migrations/versions/d1ab608c102a_.py

@@ -0,0 +1,35 @@
+"""empty message
+
+Revision ID: d1ab608c102a
+Revises: 53a175284ebe
+Create Date: 2018-11-23 23:40:00.232851
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = 'd1ab608c102a'
+down_revision = '53a175284ebe'
+branch_labels = None
+depends_on = None
+
+
+def upgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.create_table('follows',
+    sa.Column('follower_id', sa.Integer(), nullable=False),
+    sa.Column('followed_id', sa.Integer(), nullable=False),
+    sa.Column('timestamp', sa.DateTime(), nullable=True),
+    sa.ForeignKeyConstraint(['followed_id'], ['users.id'], ),
+    sa.ForeignKeyConstraint(['follower_id'], ['users.id'], ),
+    sa.PrimaryKeyConstraint('follower_id', 'followed_id')
+    )
+    # ### end Alembic commands ###
+
+
+def downgrade():
+    # ### commands auto generated by Alembic - please adjust! ###
+    op.drop_table('follows')
+    # ### end Alembic commands ###

tests/test_user_model.py

@@ -2,7 +2,7 @@ import unittest
 import time
 from datetime import datetime
 from app import create_app, db
-from app.models import User, AnonymousUser, Role, Permission
+from app.models import User, AnonymousUser, Role, Permission, Follow
 
 
 class UserModelTestCase(unittest.TestCase):
@@ -169,3 +169,40 @@ class UserModelTestCase(unittest.TestCase):
             self.assertTrue('s=256' in gravatar_256)
             self.assertTrue('r=pg'in gravatar_pg)
             self.assertTrue('d=retro' in gravatar_retro)
+
+    def test_follows(self):
+        u1 = User(email='john@example.com', password='cat')
+        u2 = User(email='susan@example.org', password='dog')
+        db.session.add(u1)
+        db.session.add(u2)
+        db.session.commit()
+        self.assertFalse(u1.is_following(u2))
+        self.assertFalse(u1.is_followed_by(u2))
+        timestamp_before = datetime.utcnow()
+        u1.follow(u2)
+        db.session.add(u1)
+        db.session.commit()
+        timestamp_after = datetime.utcnow()
+        self.assertTrue(u1.is_following(u2))
+        self.assertFalse(u1.is_followed_by(u2))
+        self.assertTrue(u2.is_followed_by(u1))
+        self.assertTrue(u1.followed.count() == 1)
+        self.assertTrue(u2.followers.count() == 1)
+        f = u1.followed.all()[-1]
+        self.assertTrue(f.followed == u2)
+        self.assertTrue(timestamp_before <= f.timestamp <= timestamp_after)
+        f = u2.followers.all()[-1]
+        self.assertTrue(f.follower == u1)
+        u1.unfollow(u2)
+        db.session.add(u1)
+        db.session.commit()
+        self.assertTrue(u1.followed.count() == 0)
+        self.assertTrue(u2.followers.count() == 0)
+        self.assertTrue(Follow.query.count() == 0)
+        u2.follow(u1)
+        db.session.add(u1)
+        db.session.add(u2)
+        db.session.commit()
+        db.session.delete(u2)
+        db.session.commit()
+        self.assertTrue(Follow.query.count() == 0)