Returning pagination metadata.

internal/data/movies.go

@@ -194,15 +194,16 @@ func (m MovieModel) Delete(id int64) error {
 }
 
 // GetAll : Returns a slice of movies. Although we're not using them right now, we've set this up to accept the various filter parameters as arguments
-func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*Movie, error) {
+func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*Movie, Metadata, error) {
 	// Construct the SQL query to retrieve all movie records.
 	// to_tsvector('simple', title) transforms 'The Breakfast Club' into 'breakfast' 'club' 'the'. The 'simple' parameter's value is the configuration.
 	// plainto_tsquery('simple', $1) takes a search value and turns it into a formatted query term that PostgreSQL full-text search can understand. As an example : "The Club" would result in the query term 'the' & 'club'
 	// The @@ operator is the matches' operator. To continue the example, the query term 'the' & 'club' will match rows which contain both lexemes 'the' and 'club'.
 	// Add an ORDER BY clause and interpolate the sort column and direction. Importantly, notice that we also include a secondary sort on the movie ID to ensure a consistent ordering.
 	// Update the SQL query to include the LIMIT and OFFSET clauses with placeholder parameter values
+	// Update the SQL query to include the window function which counts the total (filtered) records
 	query := fmt.Sprintf(`
-		SELECT id, created_at, title, year, runtime, genres, version
+		SELECT count(*) OVER(), id, created_at, title, year, runtime, genres, version
 		FROM movies
 		WHERE (to_tsvector('simple', title) @@ plainto_tsquery('simple', $1) OR $1 = '')
 		AND (genres @> $2 OR $2 = '{}')
@@ -220,12 +221,13 @@ func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*M
 	// And then pass the args slice to QueryContext() as a variadic parameter
 	rows, err := m.DB.QueryContext(ctx, query, args...)
 	if err != nil {
-		return nil, err
+		return nil, Metadata{}, err
 	}
 
 	// Importantly, defer a call to rows.Close() to ensure the resultset is closed before GetAll() returns
 	defer rows.Close()
 
+	totalRecords := 0
 	// Initialize an empty slice to hold the movie data.
 	movies := []*Movie{}
 
@@ -236,6 +238,7 @@ func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*M
 
 		// Scan the values from the row into the Movie struct. Again, note that we're using the pq.Array() adapter on the genres field here.
 		err := rows.Scan(
+			&totalRecords,
 			&movie.ID,
 			&movie.CreatedAt,
 			&movie.Title,
@@ -245,7 +248,7 @@ func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*M
 			&movie.Version,
 		)
 		if err != nil {
-			return nil, err
+			return nil, Metadata{}, err
 		}
 
 		// Add the Movie struct to the slice.
@@ -254,10 +257,14 @@ func (m MovieModel) GetAll(title string, genres []string, filters Filters) ([]*M
 
 	// When the rows.Next() loop has finished, call rows.Err() to retrieve any error that was encountered during the iteration.
 	if err = rows.Err(); err != nil {
-		return nil, err
+		return nil, Metadata{}, err
 	}
 
+	// Generate a Metadata struct, passing in the total record count and pagination parameters from the client
+	metadata := calculateMetadata(totalRecords, filters.Page, filters.PageSize)
+
 	// If everything went OK, then return the slice of movies
-	return movies, nil
+	// Include the metadata struct when returning
+	return movies, metadata, nil
 
 }