tern

Tern - The SQL Fan's Migrator

Tern is a standalone migration tool for PostgreSQL.

Installation

go get github.com/JackC/tern
go install github.com/JackC/tern

Creating a Tern Project

Tern projects are composed of a config file and a directory of migrations. See the sample directory for an example. By default tern will look in the current directory for the config file tern.conf and the migrations.

The config file requires socket or host, database, and user.

[database]
socket = /private/tmp/.s.PGSQL.5432
# host = 127.0.0.1
# port = 5432
database = tern_test
user = jack
# password = secret
# version_table = schema_version

[data]
prefix = foo

Values in the data section will be available for interpolation into migrations.

The migrations themselves have an extremely simple file format. They are simply the up and down SQL statements divided by a magic comment.

---- create above / drop below ----

Example:

create table t1(
  id serial primary key
);

---- create above / drop below ----

drop table t1;

If a migration is irreversible such as a drop table, simply delete the magic comment.

drop table widgets;

To interpolate a custom data value from the config file prefix the name with a dot and surround the whole with double curly braces.

create table {{.prefix}}config(
  id serial primary key
);

Migrations are read from files in the migration directory in lexicographic order. Typically, migration files will be prefix with 001, 002, 003, etc., but that is not strictly necessary, Each migration is run in a transaction.

Any SQL files in subdirectories of the migration directory, will be available for inclusion with the template command. This can be especially useful for definitions of views and functions that may have to be dropped and recreated when the underlying table(s) change.

// Include the file shared/v1_001.sql. Note the trailing dot.
// It is necessary if the shared file needs access to custom data values.
{{ template "shared/v1_001.sql" . }}
);

Tern uses the standard Go text/template package so conditionals and other advanced templating features are available if needed. See the package docs for details.

Migrating

To migrate up to the last version using migrations and config file located in the same directory simply run tern:

tern

To migrate up or down to a specific version:

tern --destination 42

To use a different config file:

tern --config path/to/tern.json

Embedding Tern

All the actual functionality of tern is in the github.com/JackC/tern/migrate library. If you need to embed migrations into your own application this library can help.

Prior Ruby Gem Version

The projects using the prior version of tern that was distributed as a Ruby Gem are incompatible with the version 1 release. However, that version of tern is still available through RubyGems and the source code is on the ruby branch.

Version History

1.1.0 (April 22, 2014)

• Add sub-template support
• Switch to ini for config files
• Add custom data merging

1.0.0 (April 19, 2014)

• Total rewrite in Go

0.7.1

• Print friendly error message when database error occurs instead of stack trace.

0.7.0

• Added ERB processing to SQL files

License

Copyright (c) 2011-2014 Jack Christensen, released under the MIT license