68 lines
3.5 KiB
Markdown
68 lines
3.5 KiB
Markdown
# FAQ
|
|
|
|
#### How is the code base structured?
|
|
```
|
|
/ package migrate (the heart of everything)
|
|
/cli the CLI wrapper
|
|
/database database driver and sub directories have the actual driver implementations
|
|
/source source driver and sub directories have the actual driver implementations
|
|
```
|
|
|
|
#### Why is there no `source/driver.go:Last()`?
|
|
It's not needed. And unless the source has a "native" way to read a directory in reversed order,
|
|
it might be expensive to do a full directory scan in order to get the last element.
|
|
|
|
#### What is a NilMigration? NilVersion?
|
|
NilMigration defines a migration without a body. NilVersion is defined as const -1.
|
|
|
|
#### What is the difference between uint(version) and int(targetVersion)?
|
|
version refers to an existing migration version coming from a source and therefor can never be negative.
|
|
targetVersion can either be a version OR represent a NilVersion, which equals -1.
|
|
|
|
#### What's the difference between Next/Previous and Up/Down?
|
|
```
|
|
1_first_migration.up next -> 2_second_migration.up ...
|
|
1_first_migration.down <- previous 2_second_migration.down ...
|
|
```
|
|
|
|
#### Why two separate files (up and down) for a migration?
|
|
It makes all of our lives easier. No new markup/syntax to learn for users
|
|
and existing database utility tools continue to work as expected.
|
|
|
|
#### How many migrations can migrate handle?
|
|
Whatever the maximum positive signed integer value is for your platform.
|
|
For 32bit it would be 2,147,483,647 migrations. Migrate only keeps references to
|
|
the currently run and pre-fetched migrations in memory. Please note that some
|
|
source drivers need to do build a full "directory" tree first, which puts some
|
|
heat on the memory consumption.
|
|
|
|
#### Are the table tests in migrate_test.go bloated?
|
|
Yes and no. There are duplicate test cases for sure but they don't hurt here. In fact
|
|
the tests are very visual now and might help new users understand expected behaviors quickly.
|
|
Migrate from version x to y and y is the last migration? Just check out the test for
|
|
that particular case and know what's going on instantly.
|
|
|
|
#### What is Docker being used for?
|
|
Only for testing. See [testing/docker.go](testing/docker.go)
|
|
|
|
#### Why not just use docker-compose?
|
|
It doesn't give us enough runtime control for testing. We want to be able to bring up containers fast
|
|
and whenever we want, not just once at the beginning of all tests.
|
|
|
|
#### Can I maintain my driver in my own repository?
|
|
Yes, technically thats possible. We want to encourage you to contribute your driver to this respository though.
|
|
The driver's functionality is dictated by migrate's interfaces. That means there should really
|
|
just be one driver for a database/ source. We want to prevent a future where several drivers doing the exact same thing,
|
|
just implemented a bit differently, co-exist somewhere on Github. If users have to do research first to find the
|
|
"best" available driver for a database in order to get started, we would have failed as an open source community.
|
|
|
|
#### Can I mix multiple sources during a batch of migrations?
|
|
No.
|
|
|
|
#### What does "dirty" database mean?
|
|
Before a migration runs, each database sets a dirty flag. Execution stops if a migration fails and the dirty state persists,
|
|
which prevents attempts to run more migrations on top of a failed migration. You need to manually fix the error
|
|
and then "force" the expected version.
|
|
|
|
|