This repository holds in progress and completed specification for features of MongoDB, Drivers, and associated products. Also contained is a rudimentary system for producing these documents.
When developing specifications -- and the drivers themselves -- we follow the following principles:
Strive to be idiomatic, but favor consistency
Drivers attempt to provide the easiest way to work with MongoDB in a given language ecosystem, while specifications attempt to provide a consistent behavior and experience across all languages. Drivers should strive to be as idiomatic as possible while meeting the specification and staying true to the original intent.
Too many choices stress out users. Whenever possible, we aim to minimize the number of configuration options exposed to users. In particular, if a typical user would have no idea how to choose a correct value, we pick a good default instead of adding a knob.
Users test and deploy against different topologies or might scale up from replica sets to sharded clusters. Applications should never need to use the driver differently based on topology type.
Where possible, depend on server to return errors
The features available to users depend on a server's version, topology, storage engine and configuration. So that drivers don't need to code and test all possible variations, and to maximize forward compatibility, always let users attempt operations and let the server error when it can't comply. Exceptions should be rare: for cases where the server might not error and correctness is at stake.
Minimize administrative helpers
Administrative helpers are methods for admin tasks, like user creation. These are rarely used and have maintenance costs as the server changes the administrative API. Don't create administrative helpers; let users rely on "RunCommand" for administrative commands.
Check wire version, not server version
When determining server capabilities within the driver, rely only on the maxWireVersion in the hello response, not on the X.Y.Z server version. An exception is testing server development releases, as the server bumps wire version early and then continues to add features until the GA.
When in doubt, use "MUST" not "SHOULD" in specs
Specs guide our work. While there are occasionally valid technical reasons for drivers to differ in their behavior, avoid encouraging it with a wishy-washy "SHOULD" instead of a more assertive "MUST".
While we have some idea of what the server will do in the future, don't design features with those expectations in mind. Design and implement based on what is expected in the next release.
Case Study: In designing OP_MSG, we held off on designing support for Document Sequences in Replies in drivers until the server would support it. We subsequently decided not to implement that feature in the server.
The best way to see what the server does is to test it
For any unusual case, relying on documentation or anecdote to anticipate the server's behavior in different versions/topologies/etc. is error-prone. The best way to check the server's behavior is to use a driver or the shell and test it directly.
Drivers follow semantic versioning
Drivers should follow X.Y.Z versioning, where breaking API changes require a bump to X. See semver.org for more.
Backward breaking behavior changes and semver
Backward breaking behavior changes can be more dangerous and disruptive than backward breaking API changes. When thinking about the implications of a behavior change, ask yourself what could happen if a user upgraded your library without carefully reading the changelog and/or adequately testing the change.
Store all source documents in the
Prose test numbering
When numbering prose tests, always use relative numbered bullets (
tests must be appended at the end of the test list, since drivers may refer to
existing tests by number.
Outdated tests must not be removed completely, but may be marked as such (e.g. by striking through or replacing the entire test with a note (e.g. Removed).
To build documents issue the
make command in a local copy of this
repository. The output PDFs end up in the
build/ directory. The
build depends on:
make all will build all documents in the
source/ folder. The
system builds all targets in
make setup to generate (or regenerate) a
file which provides specific targets for all files in the source file
so you can choose to compile only some of the files that you
need. Once generated, running "
will rebuild only those files (if needed.)
make clean to remove the
build/ directory and "
cleanup" to remove the LaTeX by-products from
Converting to JSON
There are many YAML to JSON converters. There are even several converters called
yaml2json in NPM. Alas, we are not using
yaml2json anymore, but instead
the js-yaml package. Use only that
converter, so that JSON is formatted consistently.
npm install -g js-yaml, then run
make in the
at the top level of this repository to convert all YAML test files to JSON.
All the specs in this repository are available under the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.