Go-Template

Introduction

This repository contains a Go code generator based on Go Template and a set of Go Template examples.

Go code generator

Go templates are one of the best choice to build a fast and small code generation tool.

The sample code generator tool presented here can generate any type of code from Go templates and json or yaml data.

Installation

Download zip archive from github or clone this repository

git clone https://github.com/phcollignon/Go-Template

Usage

You can use it as a command line or as a go library to dynamically generate code in go programs.

build the binary

Go in Go-Template/src directory.

cd Go-Template/src
go build

Add Go-Template to your binaries or to your PATH (i.e sudo mv Go-Template /usr/local/bin)

command line

Go in one of the examples directory and run Go-Template with a data file and a template file as parameters.

cd Go-Template/examples/01-values
Go-Template -d email.json -t  email.tpl

output directory

By default, generated files are created in the same folder as the json file.

You can change the ouput directory with -o outputdirectory

Go-Template -d email.json -t email.tpl -o /tmp/gocodegentest

multiple file generation

If your Json Data file is designed to generate multiple files (see Example 5 below), use the following command :

Go-Template -d mailing.json -t mailing.tpl -m multi

Examples

We provide here some code generation examples, please note that gocodgen is based on go templates, so for more advanced features, you can look at go template documentation.

01 : Simple code generation

Let's suppose the following email template :

Dear {{.Name}},

Hello, 

We would like to assign some tasks for {{.Project}} project :
{{range .Topics}}
    - {{.}}
{{end}}

Can we plan a meeting on {{.Date}} ?

Regards,

And the following data :

{
    "Name": "Phil",
    "Date": "01/01/2018",
    "Project": "Go-Template",
    "Topics": [
        "write documentation",
        "publish to github.com",
        "add more examples"
    ]
}

The following command,

Go-Template -d 01-values/email.json -t 01-values/email.tpl

generates email.generated.txt file

Dear Phil,

Hello, 

We would like to assign some tasks for Go-Template project :

    - write documentation

    - publish to github.com

    - add more examples


Can we plan a meeting on 01/01/2018 ?

Regards,

02 : Loop on Json Data

Let's suppose the following template to generate SQL code for table create :

{{range  .Schema.Table}}
	CREATE TABLE {{ .Name}} (
		{{range $idx, $column := .Column}}
			{{if  $idx }} , {{end}}{{ $column.Name}} {{$column.Type}} {{if $column.Size }} {{$column.Size}} {{end}}
		{{end}}
		)
{{end}}

And the following schema definition :

{
  "Schema": {
    "Table": [
      {
        "Name": "EMPLOYEE",
        "Column": [
          {
            "Name": "ID",
            "Type": "INTEGER"
          },
          {
            "Name": "FIRSTNAME",
            "Type": "VARCHAR",
            "Size": "256"
          },
          {
            "Name": "LASTNAME",
            "Type": "VARCHAR",
            "Size": "256"
          },
          {
            "Name": "AGE",
            "Type": "INTEGER"
          }
        ]
      },
      {
        "Name": "PRODUCT",
        "Column": [
          {
            "Name": "ID",
            "Type": "INTEGER"
          },
          {
            "Name": "NAME",
The following command,

            "Type": "VARCHAR",
            "Size": "256"
          },
          {
            "Name": "PRICE",
            "Type": "REAL"
          }
        ]
      }
    ]
  }
}

Go-Template -d schema.json -t createtable.tpl

generates the following file

	CREATE TABLE EMPLOYEE (	
			ID INTEGER 	
			 , FIRSTNAME VARCHAR  256 		
			 , LASTNAME VARCHAR  256 		
			 , AGE INTEGER 		
		)

	CREATE TABLE PRODUCT (		
			ID INTEGER 		
			 , NAME VARCHAR  256 		
			 , PRICE REAL 		
		)

03 : Add conditions and Golang template functions

Let's imagine you want to compare some numbers :

{{ range .Number}}
    {{if eq  .n1 .n2 }}
        {{- .n1}} = {{.n2}}
    {{else}}
        {{- if lt .n1 .n2 }}
            {{- .n1}} < {{.n2}}
        {{else}}
            {{- .n1}} > {{.n2}}
        {{end}}
    {{end}}
{{end}}

And the following numbers to be compared :

{
    "Number" : [
        {"n1":1,"n2":2},
        {"n1":5,"n2":3},
        {"n1":2,"n2":2},
        {"n1":1,"n2":5},
        {"n1":6,"n2":6},
        {"n1":5,"n2":2}

    ]
}

Go-Template -d numbers.json -t numbers.tpl

generates the following file

    1 < 2
    5 > 3
    2 = 2
    1 < 5
    6 = 6
    5 > 2
 

04 : Custom functions

Let's now consider a more advanced sample where you want to apply some custome functions in your code generation.

The JavaBeans setter and getter functions must be written as getPropertyName() for propertyName property.

First, add a custom function in my-funcs.go file

var MyFuncMap = map[string]interface{}{
	"ToGetterName": ToGetterName,
	"ToSetterName": ToSetterName}

func ToGetterName(name string) string {
	return "get" + strings.Title(name)
}
func ToSetterName(name string) string {
	return "set" + strings.Title(name)
}

Now you can use that custom function in your Go template :

public class User implements java.io.Serializable {
    {{range .User.Property }}
        private {{.Type}} {{ .Name  }};
    {{end}}


    {{range .User.Property }}
        public {{.Type}} {{ .Name | ToGetterName }}(){
            return this.{{.Name}};
        }
    {{end}}

    {{range .User.Property }}
        public void {{ .Name   | ToSetterName   }}({{.Type}} {{.Name}}){
            this.{{.Name}} = {{.Name}};
        }
    {{end}}
}

Either compile the gocodgen for your platform or install Go and run go run main.go my-funcs.go -d numbers.json -t numbers.tpl

For the following json data,

{
    "User": {
        "Name" : "Person",
        "Property": [
            {
               "Name": "firstName",
               "Type": "String"
            },
            {
                "Name": "lastName",
                "Type": "String"
            },
            {
                "Name": "age",
                "Type": "Integer"
            }
        ]
    }
}
 

You get this result :

public class User implements java.io.Serializable {
    
        private String firstName;
    
        private String lastName;
    
        private Integer age;
    


    
        public String getFirstName(){
            return this.firstName;
        }
    
        public String getLastName(){
            return this.lastName;
        }
    
        public Integer getAge(){
            return this.age;
        }
    

    
        public void setFirstName(String firstName){
            this.firstName = firstName;
        }
    
        public void setLastName(String lastName){
            this.lastName = lastName;
        }
    
        public void setAge(Integer age){
            this.age = age;
        }
    
}

05 : Generate multiple files

Sometime, you want to generate a set of files from some data.

The most obvious example is a mailing .. let's have the same email as in Example 01

Dear {{.Name}},

Hello, 

We would like to assign some tasks for {{.Project}} project :
{{range .Topics}}
    - {{.}}
{{end}}

Can we plan a meeting on {{.Date}} ?

Regards,

You include in your Json Data file, a Files key containing a table of objects. Each object has a FileName used to create the file, and a Data object which container the code generation data.

{
    "Files": [{
        "FileName": "test1",
        "Data": {
            "Name": "phil",
            "Date": "01/01/2018",
            "Project": "Go-Template",
            "Topics": [
                "write documentation",
                "publish to github.com",
                "add more examples"
            ]
        }
    },
    {
        "FileName": "test2",
        "Data": {
            "Name": "john",
            "Date": "01/01/2018",
            "Project": "Go-Template",
            "Topics": [
                "write documentation",
                "publish to github.com",
                "add more examples"
            ]
        }
    },
    {
        "FileName": "test3",
        "Data": {
            "Name": "peter",
            "Date": "01/01/2018",
            "Project": "Go-Template",
            "Topics": [
                "write documentation",
                "publish to github.com",
                "add more examples"
            ]
        }
    }]
}

The following command (do not forget -m multi flag) :

Go-Template -d mailing.json -t mailing.tpl -m multi

generates 3 different files :

test1 :

Dear phil,

Hello, 

We would like to assign some tasks for Go-Template project :

    - write documentation

    - publish to github.com

    - add more examples


Can we plan a meeting on 01/01/2018 ?

Regards,
 

test2 :

Dear john,

Hello, 

We would like to assign some tasks for Go-Template project :

    - write documentation

    - publish to github.com

    - add more examples


Can we plan a meeting on 01/01/2018 ?

Regards,

 

test3 :

Dear peter,

Hello, 

We would like to assign some tasks for Go-Template project :

    - write documentation

    - publish to github.com

    - add more examples


Can we plan a meeting on 01/01/2018 ?

Regards,

 

Go templates examples

Here is the list of Go template examples. You can use them in your own code or with the generator documented below.