Adding The Favorite Flag

User Favorites

One way that we could find the user’s favorites would be to run a separate MATCH clause within the same query. But as all of the routes that interact with the MovieDAO are used by both anonymous and logged in users, this could add unwanted complexity to the service.

Instead, it would be cleaner to execute two separate queries within the same transaction; one query to fetch a list of the user’s favorites, and another to retrieve a list of movies.

Fortunately, with only a few minor tweaks to the code, we can create a method that can be used to populate the favorite flag in the every other method in the MovieDAO.

Finding Favorites

Modify the get_user_favorites() method to run the following query against the tx object to return a list of IDs for each movie that the user has added to their favorites.

MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
RETURN m.tmdbId AS id

def get_user_favorites(self, tx, user_id):
    if user_id == None:
        return []

    result = tx.run("""
        MATCH (u:User {userId: $userId})-[:HAS_FAVORITE]->(m)
        RETURN m.tmdbId AS id
    """, userId=user_id)

    return [ record.get("id") for record in result ]

Multiple Transaction Calls

The get_movies function defined in the all method of the MoviesDAO already uses tx.run() to run a Cypher statement within the current transaction.

To use the list of Movie IDs in the query, you can simply add a call to the self.get_user_favorites() method above the cypher variable. The output of the function can then be passed as a named parameter in the existing call to tx.run().

All that is left to do is to add a new item to m { .* } in the Cypher statement to check whether the tmdbId property of the current movie is in the favorites array.

# Get User favorites
favorites = self.get_user_favorites(tx, user_id)

# Define the cypher statement
cypher = """
    MATCH (m:Movie)
    WHERE m.`{0}` IS NOT NULL
    RETURN m {{
        .*,
        favorite: m.tmdbId IN $favorites
    }} AS movie
    ORDER BY m.`{0}` {1}
    SKIP $skip
    LIMIT $limit
""".format(sort, order)

# Run the statement within the transaction passed as the first argument
result = tx.run(cypher, limit=limit, skip=skip, user_id=user_id, favorites=favorites)

Comparing Versions

If we take a look at the two versions of the all() method, not much has changed. The favorites array has been passed through as a parameter to the query, and the query now uses the Cypher IN clause to check if the ID is included in the array.

# Get User favorites
favorites = self.get_user_favorites(tx, user_id)

# Define the cypher statement
cypher = """
    MATCH (m:Movie)
    WHERE m.`{0}` IS NOT NULL
    RETURN m {{
        .*,
        favorite: m.tmdbId IN $favorites
    }} AS movie
    ORDER BY m.`{0}` {1}
    SKIP $skip
    LIMIT $limit
""".format(sort, order)

# Run the statement within the transaction passed as the first argument
result = tx.run(cypher, limit=limit, skip=skip, user_id=user_id, favorites=favorites)

# Define the cypher statement
cypher = """
    MATCH (m:Movie)
    WHERE m.`{0}` IS NOT NULL
    RETURN m {{ .* }} AS movie
    ORDER BY m.`{0}` {1}
    SKIP $skip
    LIMIT $limit
""".format(sort, order)

# Run the statement within the transaction passed as the first argument
result = tx.run(cypher, limit=limit, skip=skip, user_id=user_id)