My Favorites List

The My Favorites Feature

Clicking the My Favorites link in the main navigation will take you to page which contains a list of Movies that you can revisit later.

When a logged in user hovers their mouse cursor over a Movie on the website, a bookmark icon appears in the top right hand corner. Clicking this icon will either add or remove the Movie from the user’s Favorites list.

When adding a Movie to the list, a POST request it sent to the /api/favorites/{id} endpoint. When this happens, the following chain of events will occur:

Likewise, when it is clicked for a Movie that has already been favorited, a DELETE request is sent to the same URL, and the Movie is removed from the list.

Adding a Movie to My Favorites

For the first part of this challenge, modify the add() method to open a new database session, run the Cypher statement to create the :HAS_FAVORITE relationship, close the session and return the movie details along with an additional favorite property.

MATCH (u:User {userId: $userId})
MATCH (m:Movie {tmdbId: $movieId})

MERGE (u)-[r:HAS_FAVORITE]->(m)
ON CREATE SET r.createdAt = datetime()

RETURN m {
    .*,
    favorite: true
} AS movie

# Define a new transaction function to create a HAS_FAVORITE relationship
def add_to_favorites(tx, user_id, movie_id):
    row = tx.run("""
        MATCH (u:User {userId: $userId})
        MATCH (m:Movie {tmdbId: $movieId})
        MERGE (u)-[r:HAS_FAVORITE]->(m)
        ON CREATE SET u.createdAt = datetime()
        RETURN m {
            .*,
            favorite: true
        } AS movie
    """, userId=user_id, movieId=movie_id).single()

# If no rows are returnedm throw a NotFoundException
if row == None:
    raise NotFoundException()

return row.get("movie")

with self.driver.session() as session:
    return session.execute_write(add_to_favorites, user_id, movie_id)

def add(self, user_id, movie_id):
    # Define a new transaction function to create a HAS_FAVORITE relationship
    def add_to_favorites(tx, user_id, movie_id):
        row = tx.run("""
            MATCH (u:User {userId: $userId})
            MATCH (m:Movie {tmdbId: $movieId})
            MERGE (u)-[r:HAS_FAVORITE]->(m)
            ON CREATE SET u.createdAt = datetime()
            RETURN m {
                .*,
                favorite: true
            } AS movie
        """, userId=user_id, movieId=movie_id).single()

        # If no rows are returnedm throw a NotFoundException
        if row == None:
            raise NotFoundException()

        return row.get("movie")

    with self.driver.session() as session:
        return session.execute_write(add_to_favorites, user_id, movie_id)

Removing a Movie from My Favorites

The second part of this challenge is to write the code to remove a movie from the My Favorites list.

The code for deleting the :HAS_FAVORITE relationship will be similar, only the Cypher statement will change.

Instead of two separate MATCH clauses, we can instead attempt to find the pattern within a single clause. If the relationship (with an alias of r) exists, we will delete it and then return the movie information with favorite set to false.

MATCH (u:User {userId: $userId})-[r:HAS_FAVORITE]->(m:Movie {tmdbId: $movieId})
DELETE r

RETURN m {
    .*,
    favorite: false
} AS movie

Use the code from the add() method above to implement the remove() function. If you get stuck, you can reveal the completed method below.

def remove(self, user_id, movie_id):
    # Define a transaction function to delete the HAS_FAVORITE relationship within a Write Transaction
    def remove_from_favorites(tx, user_id, movie_id):
        row = tx.run("""
            MATCH (u:User {userId: $userId})-[r:HAS_FAVORITE]->(m:Movie {tmdbId: $movieId})
            DELETE r
            RETURN m {
                .*,
                favorite: false
            } AS movie
        """, userId=user_id, movieId=movie_id).single()

        # If no rows are returnedm throw a NotFoundException
        if row == None:
            raise NotFoundException()

        return row.get("movie")

    # Execute the transaction function within a Write Transaction
    with self.driver.session() as session:
        # Return movie details and `favorite` property
        return session.execute_write(remove_from_favorites, user_id, movie_id)

Listing My Favorites

Finally, the all() method in the FavoriteDAO currently returns a hardcoded list of Movies.

def all(self, user_id, sort = 'title', order = 'ASC', limit = 6, skip = 0):
    # TODO: Open a new session
    # TODO: Retrieve a list of movies favorited by the user
    return popular

Update this method to return a paginated list of movies that the user has added to their My Favorites list.

MATCH (u:User {userId: $userId})
MATCH (m:Movie {tmdbId: $movieId})

MERGE (u)-[r:HAS_FAVORITE]->(m)
ON CREATE SET r.createdAt = datetime()

RETURN m {
    .*,
    favorite: true
} AS movie

This time, as the query is simpler, you can use a lambda function to represent the transaction function.

# Retrieve a list of movies favorited by the user
movies = session.execute_read(lambda tx: tx.run("""
    MATCH (u:User {{userId: $userId}})-[r:HAS_FAVORITE]->(m:Movie)
    RETURN m {{
        .*,
        favorite: true
    }} AS movie
    ORDER BY m.`{0}` {1}
    SKIP $skip
    LIMIT $limit
""".format(sort, order), userId=user_id, limit=limit, skip=skip).value("movie"))

def all(self, user_id, sort = 'title', order = 'ASC', limit = 6, skip = 0):
    # Open a new session
    with self.driver.session() as session:
        # Retrieve a list of movies favorited by the user
        movies = session.execute_read(lambda tx: tx.run("""
            MATCH (u:User {{userId: $userId}})-[r:HAS_FAVORITE]->(m:Movie)
            RETURN m {{
                .*,
                favorite: true
            }} AS movie
            ORDER BY m.`{0}` {1}
            SKIP $skip
            LIMIT $limit
        """.format(sort, order), userId=user_id, limit=limit, skip=skip).value("movie"))

        return movies

Testing

To test that this functionality has been correctly implemented, run the following code in a new terminal session:

pytest tests/07_favorites_list__test.py

The test file is located at tests/07_favorites_list__test.py.

git checkout 07-favorites-list