README.md

Go - GenMapping

This project is a struct to struct mapping code generator for Go.

Concept

GenMapping analyzes a Go module and searches for interfaces which describe desired mapping operations. GenMapping generates mapper based on those interfaces. The generation can be configured with tag documentation.

All mappers can also cross-reference themselves in the mapping process:

type Foo struct {
  A Bar
}

type Foo2 struct {
  A Bar2
} 

type Bar struct {}
type Bar2 struct {}

When you create a mapper for Bar to Bar2, the mapper for Foo to Foo2 can use that already defined mapper, removing the necessity to write that logic yourself

Tags

Tags are comment annotations which instruct GenMapping how to generate the mapper functions.

Documentation for Tags can be found in documentation/Tags.mnd

Syntax

A mapper is a simple Go interface annotated with the @mapper tag. This tag tells GenMapping, that this interface describes mapping functions.

Mapping functions have the following rules:

• Only 1 return is allowed (error handling is planned in a future update)
• It has to be exported
• It can have any number of parameters

Mapping function cross-reference has stricter rules:

• Only 1 parameter is allowed (Source Type)

Examples

Structures used in the examples can be found under test/

Given a mapper interface like this:

// SensorMapper
// @mapper
type SensorMapper interface {

	//BoToDto
	//@translate(from="sensor.ComplicatedObject.BoSimple", to="ComplicatedObject.DtoSimple")
	BoToDto(sensor bo.Sensor) dto.Sensor
}

// PropertyMapper
// @mapper
type PropertyMapper interface {

	//BoToDto
	//@translate(from="property.BoSimple", to="DtoSimple")
	BoToDto(property bo.Property) dto.Property
}

GenMapping will generate a mapper function like this:

package SensorMapper

import (
	"GenMapping/test/bo"
	"GenMapping/test/dto"
	"GenMapping/test/mapper/PropertyMapper"
)

//SensorMapper:

func BoToDto(sensor bo.Sensor) (target dto.Sensor) {
	target.Simple = sensor.Simple
	target.SimplePtr = sensor.SimplePtr
	target.SimpleString = sensor.SimpleString
	target.ComplicatedObject = PropertyMapper.BoToDto(sensor.ComplicatedObject)
	target.ComplicatedObject.DtoSimple = sensor.ComplicatedObject.BoSimple
	//target.ComplicatedObject.DoubleTest is not directly mapped
	//target.ComplicatedObject.Time is not directly mapped
	for i0 := range target.PropertyArray {
		target.PropertyArray[i0] = PropertyMapper.BoToDto(sensor.ComplicatedObject)
		//target.PropertyArray[i0].DtoSimple is not directly mapped
		//target.PropertyArray[i0].DoubleTest is not directly mapped
		//target.PropertyArray[i0].Time is not directly mapped
	}
	return
}

//-------------------------------------
package PropertyMapper

import (
  "GenMapping/test/bo"
  "GenMapping/test/dto"
)

//PropertyMapper:

func BoToDto(property bo.Property) (target dto.Property) {
	target.DtoSimple = property.BoSimple
	target.DoubleTest = property.DoubleTest
	target.Time = property.Time
	return
}

To Do:

The following things are still not done (*) or are yet untested (°)

• Pointer Type check*
  • Mapping to pointers is still missing some type checks and eventual (de-)referencing between pointer and non pointer
• Maps*
  • map[X]Y mapping is not yet supported
• Ignored Fields*
  • Some fields should not be touched during mapping (Ids from database objects for example), thus needing a "ignore" tag for such fields
• Tag "inheritance" or groups*
  • Some mappers can share tags - allowing for referencable groups minimizes possible code duplications
• Custom mapper file paths°
  • These should work, but some edge cases could break the resulting output