Category Archives: critiquebrainz

GSoC 2017: Rating System in CritiqueBrainz


I am Pinank Solanki, an undergrad at Indian Institute of Technology (IIT) Mandi, India. I worked with the MetaBrainz Foundation on one of its projects, as part of the Google Summer of Code 2017 over the last summer. It was one of the best and exciting summers I ever had.

Let me begin from the beginning. I first came to know about MusicBrainz in January and first contacted the community in February and was immediately hooked. Initially I decided to make a proposal for addition of book reviews for CritiqueBrianz, but it was not possible because the BookBrainz web service was unstable and the CritiqueBrainz’s host didn’t have direct access to BookBrainz database. So I tried to pitch my own ideas. But then, in one of the weekly meetings, I saw great support and enthusiasm among the community members for rating system for reviews —and I personally liked the idea of the project and thought it would be a great addition to CritiqueBrainz. I submitted my proposal, got accepted and a treat to the friends was due!


The aim of the project was to add support for three types of reviews: text, rating, text+rating (CB supported only-text reviews).

The schema changes and data-access functions are completed and merged. The frontend part is mainly completed including the fundamental functionality along with additional features. It took a lot of time to select and modify the rating input plugin perfectly satisfying the project’s needs. There is still some work to be done, most of which is based on the rating scale conversion in db package. Similarly, most of the web service part is completed and is held up due to the rating scale conversion PR.


Schema changes

The schema changes done are quite different than what was mentioned in the proposal. My mentor for the project, Roman Tsukanov (Gentlecat), recommended some changes which would make keeping track of revisions a lot easier. You can see the schema here and the PR here.

Data-access functions

By the time I started working on the project, CB has migrated off the ORM. So, I wrote raw SQL queries and its tests. See the PR here. The rating scale was decided to be 1-5 but for storage a scale of 0-100 is used just like MusicBrainz keeping the possibility of migration of ratings from MB to CB in mind (more info at CB-245). This part is covered in the PR here.

Changes in user-interface

This plugin is used for rendering the rating star icons. The code can be seen in this PR. See the images below to get a good idea about the implementation.

Write review page:


Review page:


Entity page:


Revision comparison:


Web service

All the functionalities added to CritiqueBrainz had to be implemented in the web service (API) as well. All three types of reviews and other features are now supported via the web service. See the PR here.


The chief part of the documentation was to update the schema. Other than that, rating parameter and several notes were added to the API documentation. See the PR here.

Other PRs relevant to the project can be found here.

Future work

First of all, I will complete the leftover work. Web service and frontend PRs are dependent on the rating scale PR. Once it gets merged, it’s 2–3 days of work to complete the rest.

Other than that, I look forward to keep contributing to CritiqueBrainz and other MetaBrainz projects. I am sure many interesting ideas will be discussed at the annual MetaBrainz Summit in Barcelona.


It was quite an eventful summer and GSoC was the biggest of them. Thanks to Roman for his constant help and guidance over the entire summer and also to all the other community members. It was so cool to work on an open-source project and I would definitely suggest for any music and data lover to explore the MetaBrainz projects.

GSoC 2017: Directly accessing MusicBrainz DB in CritiqueBrainz

Hello, everyone! This summer was fantastic for me!
I’m Suyash Garg, an undergraduate at National Institute of Technology, Hamirpur and I participated in Google Summer of Code 2017 contributing code to CritiqueBrainz. Alastair Porter mentored me during this GSoC programme. This post summarizes my contributions to the project and experiences that I had throughout the summer.

I started contributing to CritiqueBrainz in January, 2017 and before the start of the SoC programme, I mainly worked on writing raw SQL for retrieving data from the CB database and replacing the ORM code (CB-230). Other than that I worked on issues like CB-120, CB-235 and other minor bugs and issues. They were my first proper contributions to the open source world. Thank you MetaBrainz!!

For the Google Summer of Code 2017, my project involved retrieving data related to various entities (release-groups, artists, releases, events and places) directly from the MusicBrainz database instead of querying the MusicBrainz web service (CB-231). This became necessary as some pages on CB required to fetch too much data and thus made many requests to the MB web service. These pages were taking a long time to load. Thus, by connecting directly to the database, we could reduce the load time of these pages.

Here is a summary of my contributions to the project during the summer:

Accessing the MusicBrainz database
New Infrastructure is allowing us to easily read data directly from the MusicBrainz database. For accessing the database in the development environment, another service running the MusicBrainz database was added which uses an existing Docker image which the MusicBrainz project was already using. This allowed us to share resources between projects. I worked on adding an option to download the database dumps and import the data into the database (see PR#523). Also, I added the service in CB docker-compose files and updated the documentation for setting up the development environment (see PR#115 and PR#92).
Fetching data using mbdata.models
After setting up the development environment, my mentor suggested to me to use the mbdata package for writing queries to fetch data from the database instead of writing raw SQL. I worked on retrieving information for the entity: places and added helpers for fetching the relationship information. Following that, I worked on retrieving information for other entities (release-groups, releases, events, and artists). Also, since SQLAlchemy makes lazy queries to the database, a number of queries were being issued to the database. This could slow things down as for each query it was going to require one trip to the SQL server (network trip in production). So, as suggested by my mentor, I also worked on reducing the number of queries made for fetching data related to each entity (see PR#135). For pages that made a number of requests to the web service, I made this PR#121 for fetching information related to multiple entities at the same time.
For testing, the database queries are mocked using the unittest.mock Python package. The tests added make sure that the code (serializing RowProxy objects to dictionaries, caching, etc.) works properly (see PR#134). Adding up a new service (as a separate Docker container) in the test environment and running tests was taking too much time (in creating the tables and truncating them). So as suggested by my mentors, mocking the database queries was the best option. Throughout my GSoC period, I learned how important it was to write tests (especially when you break things more when you fix something) and make them run fast. I learned that «If tests don’t run fast, they would be a distraction rather than a help» (quoting from the book “The Art of Agile Development” by James Shore).

Other than these, I also worked on some UI/UX issues, namely CB-80 (adding option to filter releases with reviews), CB-84 (ordering release groups according to release year) and CB-261 (authenticating requests to Spotify Web API). CB-130 (reviewing entities with MBID redirects – see PR#145) was also solved while solving a production server issue.

This summer was awesome for me. I learned a lot of new things and techniques for writing better code. Thanks to my mentors, Alastair Porter and Roman Tsukanov. Also, great thanks to the lovely MetaBrainz community and Google for this opportunity. I’m really looking forward to keep contributing to CritiqueBrainz and to dive into other MetaBrainz projects.