yo

yo is a command-line tool to generate Go code for Google Cloud Spanner. forked from xo 🌹

yo uses database schema to generate code by using Information Schema. yo runs SQL queries against tables in INFORMATION_SCHEMA to fetch metadata for a database, and applies the metadata to Go templates to generate code/models to acccess Cloud Spanner.

Installation

$ go get -u go.mercari.io/yo

Quickstart

The following is a quick overview of using yo on the command-line:

# change to project directory
$ cd $GOPATH/src/path/to/project

# make an output directory
$ mkdir -p models

# generate code for a schema
$ yo $PROJECT_NAME $INSTANCE_NAME $DATABASE_NAME -o models

Command Line Options

The following are yo's command-line arguments and options:

$ yo --help
yo is a command-line tool to generate Go code for Google Cloud Spanner.

Usage:
  yo PROJECT_NAME INSTANCE_NAME DATABASE_NAME [flags]

Examples:
  # Generate models under models directory
  yo $PROJECT_NAME $INSTANCE_NAME $DATABASE_NAME -o models

  # Generate models under models directory with custom types
  yo $PROJECT_NAME $INSTANCE_NAME $DATABASE_NAME -o models --custom-types-file custom_column_types.yml

Flags:
      --custom-type-package string   Go package name to use for custom or unknown types
      --custom-types-file string     custom table field type definition file
  -h, --help                         help for yo
      --ignore-fields stringArray    fields to exclude from the generated Go code types
      --ignore-tables stringArray    tables to exclude from the generated Go code types
  -o, --out string                   output path or file name
  -p, --package string               package name used in generated Go code
      --single-file                  toggle single file output
      --suffix string                output file suffix (default ".yo.go")
      --tags string                  build tags to add to package header
      --template-path string         user supplied template path

Genearated code

yo generates a file per a table by default. Each files has struct, metadata, methods for a table.

struct

From this table definition:

CREATE TABLE Examples (
  PKey STRING(32) NOT NULL,
  Num INT64 NOT NULL,
  CreatedAt TIMESTAMP NOT NULL,
) PRIMARY KEY(PKey);

This struct is generated:

type Example struct {
	PKey      string    `spanner:"PKey" json:"PKey"`           // PKey
	Num       int64     `spanner:"Num" json:"Num"`             // Num
	CreatedAt time.Time `spanner:"CreatedAt" json:"CreatedAt"` // CreatedAt
}

Mutation methods

An operation agaist a table is represented as mutation in Cloud Spanner. yo generates methods to create mutation to modify a table.

Insert
- A wrapper method of spanner.Insert, which embeds struct values implicitly to insert a new record with struct values.
Update
- A wrapper method of spanner.Update, which embeds struct values implicitly to update all columns into struct values.
InsertOrUpdate
- A wrapper method of spanner.InsertOrUpdate, which embeds struct values implicitly to insert a new record or update all columns to struct values.
UpdateColumns
- A wrapper method of spanner.Update, which updates specified columns into struct values.

Read functions

yo generates functions to read data from Cloud Spanner. The functions are generated based on index.

Naming convention of genearted functions is FindXXXByYYY. The XXX is table name and YYY is index name. XXX will be singular if the index is unique index, or plural if the index is not unique.

TODO

Generated functions use Query only even if it is secondary index. Need a function to use Read.

Error handling

yo wraps all errors as internal yoError. It has some methods for error handling.

GRPCStatus()
- This returns gRPC's *status.Status. It is intended by used from status google.golang.org/grpc/status package.
DBTableName()
- A table name where the error happens.
NotFound()
- A helper to check the error is NotFound.

The yoError inherits an original error from google-cloud-go. It stil can be used with status.FromError or status.Code to check status code of the error. So the typical error handling will be like:

result, err := SomeFunction()
if err != nil {
	code := status.Code(err)
	if code == codes.InvalidArgument {
		// error handling for invalid argument
	}
	...
	panic("unexpected")
}

Templates for code generation

yo uses Go template package to generate code. You can use your own template for code generation by using --template-path option.

yo provides default templates and uses them when --template-path option is not specified. The templates exist in templates directory. The templates are embeded into yo binary.

Custom Template Quickstart

The following is a quick overview of copying the base templates contained in the yo project's templates/ directory, editing to suit, and using with yo:

# change to working project directory
$ cd $GOPATH/src/path/to/my/project

# create a template directory
$ mkdir -p templates

# copy yo templates
$ cp "$GOPATH/src/go.mercari.io/yo/templates/*" templates/

# remove yo binary data
$ rm templates/*.go

# edit base templates
$ vi templates/*.tpl.go

# use with yo
$ yo $PROJECT_NAME $INSTANCE_NAME $DATABASE_NAME -o models --template-path templates

See the Custom Template example below for more information on adapting the base templates in the yo source tree for use within your own project.

Template files

Template File	Description
`templates/type.go.tpl`	Template for schema tables
`templates/index.go.tpl`	Template for schema indexes
`templates/yo_db.go.tpl`	Package level template generated once per package
`templates/yo_package.go.tpl`	File header template generated once per file

Helpers functions

This is not a stable feature

yo provides some helper functions which can be used in templates. Those are defined in generator/funcs.go. Those are not well documented and are likely to change.

Contribution

Please read the CLA below carefully before submitting your contribution.

https://www.mercari.com/cla/

License

yo is released under the MIT License.

GincoInc/yo

yo