POP

A Tasty Treat For All Your Database Needs

So what does Pop do exactly? Well, it wraps the absolutely amazing https://github.com/jmoiron/sqlx library. It cleans up some of the common patterns and workflows usually associated with dealing with databases in Go.

Pop makes it easy to do CRUD operations, run migrations, and build/execute queries. Is Pop an ORM? I'll leave that up to you, the reader, to decide.

Pop, by default, follows conventions that were defined by the ActiveRecord Ruby gem, http://www.rubyonrails.org. What does this mean?

• Tables must have an "id" column and a corresponding "ID" field on the struct being used.
• If there is a timestamp column named "created_at", "CreatedAt" on the struct, it will be set with the current time when the record is created.
• If there is a timestamp column named "updated_at", "UpdatedAt" on the struct, it will be set with the current time when the record is updated.
• Default database table names are lowercase, plural, and underscored versions of the struct name. Examples: User{} is "users", FooBar{} is "foo_bars", etc...

Supported Databases

• PostgreSQL (>= 9.3)
• MySQL (>= 5.7)
• SQLite (>= 3.x)
• CockroachDB (>= 1.1.1)

Connecting to Databases

Pop is easily configured using a YAML file. The configuration file should be stored in config/database.yml or database.yml.

Example Configuration File

development:
  dialect: "postgres"
  database: "your_db_development"
  host: "localhost"
  port: "5432"
  user: "postgres"
  password: "postgres"

test:
  dialect: "mysql"
  database: "your_db_test"
  host: "localhost"
  port: "3306"
  user: "root"
  password: "root"

staging:
  dialect: "sqlite3"
  database: "./staging.sqlite"

production:
  dialect: "postgres"
  url: {{ env "DATABASE_URL" }}

Note that the database.yml file is also a Go template, so you can use Go template syntax. There are two special functions that are included, env and envOr.

• env - This function will look for the named environment variable and insert it into your file. This is useful for configuring production databases without having to store secret information in your repository. {{ env "DATABASE_URL" }}
• envOr - This function will look for the named environment variable and use it. If the variable can not be found a default value will be used. {{ envOr "MYSQL_HOST" "localhost" }}

You can generate a default configuration file using the init command:

$ soda g config

The default will generate a database.yml file in the current directory for a PostgreSQL database. You can override the type of database using the -t flag and passing in any of the supported database types: postgres, cockroach, mysql, or sqlite3.

CockroachDB currently works best if you DO NOT use a url and instead define each key item. Because CockroachDB more or less uses the same driver as postgres you have the same configuration options for both. In production you will also want to make sure you are using a secure cluster and have set all the needed connection parameters for said secure connection. If you do not set the sslmode or set it to disable this will put dump and load commands into --insecure mode.

In your code

Once you have a configuration file defined you can easily connect to one of these connections in your application.

db, err := pop.Connect("development")
if err != nil {
  log.Panic(err)
}

Now that you have your connection to the database you can start executing queries against it.

CLI Support

Pop features CLI support via the soda command for the following operations:

• creating databases
• dropping databases
• migrating databases

Installing CLI Support

Without sqlite 3 support:

$ go get github.com/gobuffalo/pop/...
$ go install github.com/gobuffalo/pop/soda

with sqlite 3 support:

$ go get -u -v -tags sqlite github.com/gobuffalo/pop/...
$ go install github.com/gobuffalo/pop/soda

If you're not building your code with buffalo build, you'll also have to pass -tags sqlite to go build when building your program.

Creating Databases

Assuming you defined a configuration file like that described in the above section you can automatically create those databases using the soda command:

Create All Databases

$ soda create -a

Create a Specific Database

$ soda create -e development

Dropping Databases

Assuming you defined a configuration file like that described in the above section you can automatically drop those databases using the soda command:

Drop All Databases

$ soda drop -a

Drop a Specific Database

$ soda drop -e development

Models

The soda command supports the generation of models.

A full list of commands available for model generation can be found by asking for help:

$ soda generate help

Generate Models

The soda command will generate Go models and, optionally, the associated migrations for you.

$ soda generate model user name:text email:text

Running this command will generate the following files:

models/user.go
models/user_test.go
migrations/20170115024143_create_users.up.fizz
migrations/20170115024143_create_users.down.fizz

The models/user.go file contains a structure named User with fields ID, CreatedAt, UpdatedAt, Name, and Email. The first three correspond to the columns commonly found in ActiveRecord models as mentioned before, and the last two correspond to the additional fields specified on the command line. The known types are:

• text (string in Go)
• blob ([]byte in Go)
• time or timestamp (time.Time)
• nulls.Text (nulls.String) which corresponds to a nullifyable string, which can be distinguished from an empty string
• uuid (uuid.UUID)
• Other types are passed thru and are used as Fizz types.

The models/user_test.go contains tests for the User model and they must be implemented by you.

The other two files correspond to the migrations as explained below.

Migrations

The soda command supports the creation and running of migrations.

A full list of commands available for migration can be found by asking for help:

$ soda migrate --help

Create Migrations

The soda command will generate SQL migrations (both the up and down) files for you.

$ soda generate fizz name_of_migration

Running this command will generate the following files:

./migrations/20160815134952_name_of_migration.up.fizz
./migrations/20160815134952_name_of_migration.down.fizz

The generated files are fizz files. Fizz lets you use a common DSL for generating migrations. This means the same .fizz file can be run against any of the supported dialects of Pop! Find out more about Fizz

If you want to generate old fashion .sql files you can use the -t flag for that:

$ soda generate sql name_of_migration

Running this command will generate the following files:

./migrations/20160815134952_name_of_migration.up.sql
./migrations/20160815134952_name_of_migration.down.sql

The soda migrate command supports both .fizz and .sql files, so you can mix and match them to suit your needs.

Running Migrations

The soda command will run the migrations using the following command:

$ soda migrate up

Migrations will be run in sequential order. The previously run migrations will be kept track of in a table named schema_migrations in the database.

Migrations can also be run in reverse to rollback the schema.

$ soda migrate down

Find

user := models.User{}
err := tx.Find(&user, id)

Query

tx := models.DB
query := tx.Where("id = 1").Where("name = 'Mark'")
users := []models.User{}
err := query.All(&users)

err = tx.Where("id in (?)", 1, 2, 3).All(&users)

Join Query

// page: page number
// perpage: limit
roles := []models.UserRole{}
query := models.DB.LeftJoin("roles", "roles.id=user_roles.role_id").
  LeftJoin("users u", "u.id=user_roles.user_id").
  Where(`roles.name like ?`, name).Paginate(page, perpage)

count, _ := query.Count(models.UserRole{})
count, _ := query.CountByField(models.UserRole{}, "*")
sql, args := query.ToSQL(&pop.Model{Value: models.UserRole{}}, "user_roles.*",
  "roles.name as role_name", "u.first_name", "u.last_name")
//log.Printf("sql: %s, args: %v", sql, args)
err := models.DB.RawQuery(sql, args...).All(&roles)

Eager Loading

pop allows you to perform an eager loading for associations defined in a model. By using pop.Connection.Eager() function plus some fields tags predefined in your model you can extract associated data from a model.

type User struct {
  ID           uuid.UUID
  Email        string
  Password     string
  Books        Books     `has_many:"books" order_by:"title asc"`
  FavoriteSong Song      `has_one:"song" fk_id:"u_id"`
  Houses       Addresses `many_to_many:"users_addresses"`
}

type Book struct {
  ID      uuid.UUID
  Title   string
  Isbn    string
  User    User        `belongs_to:"user"`
  UserID  uuid.UUID
  Writers Writers     `has_many:"writers"`
}

type Writer struct {
   ID     uuid.UUID   `db:"id"`
   Name   string      `db:"name"``
   BookID uuid.UUID   `db:"book_id"`
   Book   Book        `belongs_to:"book"`
}

type Song struct {
  ID      uuid.UUID
  Title   string
  UserID  uuid.UUID   `db:"u_id"`
}

type Address struct {
  ID           uuid.UUID
  Street       string
  HouseNumber  int
}

type Addresses []Address

has_many: will load all records from the books table that have a column named user_id or the column specified with fk_id that matches the User.ID value.

belongs_to: will load a record from users table that have a column named id that matches with Book.UserID value.

has_one: will load a record from the songs table that have a column named user_id or the column specified with fk_id that matches the User.ID value.

many_to_many: will load all records from the addresses table through the table users_addresses. Table users_addresses MUST define address_id and user_id columns to match User.ID and Address.ID values. You can also define a fk_id tag that will be used in the target association i.e addresses table.

fk_id: defines the column name in the target association that matches model ID. In the example above Song has a column named u_id that represents id of users table. When loading FavoriteSong, u_id will be used instead of user_id.

 order_by: used in has_many and many_to_many to indicate the order for the association when loading. The format to use is order_by:"<column_name> <asc | desc>"

u := Users{}
err := tx.Eager().Where("name = 'Mark'").All(&u)  // preload all associations for user with name 'Mark', i.e Books, Houses and FavoriteSong
err  = tx.Eager("Books").Where("name = 'Mark'").All(&u) // preload only Books association for user with name 'Mark'.

Eager Loading Nested Associations

pop allows you to eager loading nested associations by using . character to concatenate them. Take a look at the example bellow.

tx.Eager("Books.User").First(&u)  // will load all Books for u and for every Book will load the user which will be the same as u.

 tx.Eager("Books.Writers").First(&u)  // will load all Books for u and for every Book will load all Writers.

tx.Eager("Books.Writers.Book").First(&u)  // will load all Books for u and for every Book will load all Writers and for every writer will load the Book association.

tx.Eager("Books.Writers").Eager("FavoriteSong").First(&u)  // will load all Books for u and for every Book will load all Writers. And Also it will load the favorite song for user.

Callbacks

Pop provides a means to execute code before and after database operations. This is done by defining specific methods on your models. For example, to hash a user password you may want to define the following method:

type User struct {
	ID       uuid.UUID
	Email    string
	Password string
}

func (u *User) BeforeSave(tx *pop.Connection) error {
	hash, err := bcrypt.GenerateFromPassword([]byte(u.Password), bcrypt.DefaultCost)
	if err != nil {
		return errors.WithStack(err)
	}

	u.Password = string(hash)

	return nil
}

The available callbacks include:

• BeforeSave
• BeforeCreate
• BeforeUpdate
• BeforeDestroy
• AfterSave
• AfterCreate
• AfterUpdate
• AfterDestroy
• AfterFind

Further reading

The Unofficial pop Book: a gentle introduction to new users.