fields/README.md

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# golang convert fields lib

## Idea
Main idea was to build a lib/helper to simplify copying same-name fields from one struct object to another one.

## Examples
### Example 1: most common usage, with sub-cases
```go
import (
	"log"
	"encoding/json"

	"github.com/go-convert/fields"
)

type FromStruct struct {
	ID     string `conv:"new,update"`
	Field1 string `conv:"new,update"`
	Field2 string `conv:"update"`
}

type ToStruct struct {
	ID     string
	Field1 string
	Field2 string
	Field3 string
}

func main() {
	fromDefault := FromStruct{
		"1", "field 1 value", "field 2 value",
	}
	toDefault := ToStruct{
		"old val 1", "old field 1 value", "old field 2 value", "old field 3 value",
	}

	log.Print("example 1.1 - new")
	from := fromDefault
	to := toDefault

	fields.Сonvert(from, "new", &to)
	fromB, _ := json.Marshal(from)
	toB, _ := json.Marshal(to)

	log.Printf("from %s => to %s", string(fromB), string(toB))

	log.Print("example 1.2 - update")
	from = fromDefault
	to = toDefault

	fields.Сonvert(from, "update", &to)
	fromB, _ = json.Marshal(from)
	toB, _ = json.Marshal(to)

	log.Printf("from %s => to %s", string(fromB), string(toB))
}
```
After running `go run examples/example-1/main.go`

Result will be something like below:
```bash
2020/01/14 21:46:32 example 1.1 - new
2020/01/14 21:46:32 from {"ID":"1","Field1":"field 1 value","Field2":"field 2 value"} => to {"ID":"1","Field1":"field 1 value","Field2":"old field 2 value","Field3":"old field 3 value"}
2020/01/14 21:46:32 example 1.2 - update
2020/01/14 21:46:32 from {"ID":"1","Field1":"field 1 value","Field2":"field 2 value"} => to {"ID":"1","Field1":"field 1 value","Field2":"field 2 value","Field3":"old field 3 value"}
```

### Example 2: custom config setup usage, with sub-cases
* New name of tag: `copy`
* New tag value for omitting: `ignore`
* New tag value for omitting empty field: `noempty`

```go
import (
	"log"
	"encoding/json"

	"github.com/go-convert/fields"
)

type FromStructCustom struct {
	ID     string `copy:"new,update"`
	Field1 string `copy:"new,update"`
	Field2 string `copy:"update"`
	Field3 string `copy:"category-1,ignore"`
	Field4 string `copy:"category-1,noempty"`
}

type ToStruct struct {
	ID     string
	Field1 string
	Field2 string
	Field3 string
	Field4 string
}

func main() {
	fields.SetTagName("copy")
	fields.SetOmitTagName("ignore")
	fields.SetOmitEmptyTagName("noempty")

	log.Print("example 2.1 - new")
	from := FromStructCustom{
		"1", "field 1 value", "field 2 value", "omitting", "not empty",
	}
	to := ToStruct{
		"old val 1", "old field 1 value", "old field 2 value", "old field 3 value", "old field 4 value",
	}

	fields.Сonvert(from, "new", &to)
	fromB, _ := json.Marshal(from)
	toB, _ := json.Marshal(to)

	log.Printf("from %s => to %s", string(fromB), string(toB))

	log.Print("example 2.2.1 - category-1")
	from = FromStructCustom{
		"1", "field 1 value", "field 2 value", "omitting", "not empty",
	}
	to = ToStruct{
		"old val 1", "old field 1 value", "old field 2 value", "old field 3 value", "old field 4 value",
	}

	fields.Сonvert(from, "category-1", &to)
	fromB, _ = json.Marshal(from)
	toB, _ = json.Marshal(to)

	log.Printf("from %s => to %s", string(fromB), string(toB))

	log.Print("example 2.2.2 - category-1")
	from = FromStructCustom{
		"1", "field 1 value", "field 2 value", "omitting", "",
	}
	to = ToStruct{
		"old val 1", "old field 1 value", "old field 2 value", "old field 3 value", "old field 4 value",
	}

	fields.Сonvert(from, "category-1", &to)
	fromB, _ = json.Marshal(from)
	toB, _ = json.Marshal(to)

	log.Printf("from %s => to %s", string(fromB), string(toB))
}
```
After running `go run examples/example-1/main.go`

Result will be something like below:
```bash
2020/01/14 23:13:26 example 2.1 - new
2020/01/14 23:13:26 from {"ID":"1","Field1":"field 1 value","Field2":"field 2 value","Field3":"omitting","Field4":"not empty"} => to {"ID":"1","Field1":"field 1 value","Field2":"old field 2 value","Field3":"old field 3 value","Field4":"old field 4 value"}
2020/01/14 23:13:26 example 2.2.1 - category-1
2020/01/14 23:13:26 from {"ID":"1","Field1":"field 1 value","Field2":"field 2 value","Field3":"omitting","Field4":"not empty"} => to {"ID":"old val 1","Field1":"old field 1 value","Field2":"old field 2 value","Field3":"old field 3 value","Field4":"not empty"}
2020/01/14 23:13:26 example 2.2.2 - category-1
2020/01/14 23:13:26 from {"ID":"1","Field1":"field 1 value","Field2":"field 2 value","Field3":"omitting","Field4":""} => to {"ID":"old val 1","Field1":"old field 1 value","Field2":"old field 2 value","Field3":"old field 3 value","Field4":"old field 4 value"}
```

## License
Copyright (c) 2020 Alex aka mailoman <alex@webz.asia>

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.