diff

A library for diffing golang structures and values.

Utilizing field tags and reflection, it is able to compare two structures of the same type and create a changelog of all modified values. The produced changelog can easily be serialized to json.

Build status

• Master

Installation

go get github.com/r3labs/diff

Changelog Format

When diffing two structures using Diff, a changelog will be produced. Any detected changes will populate the changelog array with a Change type:

type Change struct {
	Type string      // The type of change detected; can be one of create, update or delete
	Path []string    // The path of the detected change; will contain any field name or array index that was part of the traversal
	From interface{} // The original value that was present in the "from" structure
	To   interface{} // The new value that was detected as a change in the "to" structure
}

Given the example below, we are diffing two slices where the third element has been removed:

from := []int{1, 2, 3, 4}
to := []int{1, 2, 4}

changelog, _ := diff.Diff(from, to)

The resultant changelog should contain one change:

Change{
    Type: "delete",
    Path: ["2"],
    From: 3,
    To:   nil,
}

Supported Types

A diffable value can be/contain any of the following types:

• struct
• slice
• string
• int
• bool
• map
• pointer

Tags

In order for struct fields to be compared, they must be tagged with a given name. All tag values are prefixed with diff. i.e. diff:"items".

• - : In the event that you want to exclude a value from the diff, you can use the tag diff:"-" and the field will be ignored.

• identifier : If you need to compare arrays by a matching identifier and not based on order, you can specify the identifier tag. If an identifiable element is found in both the from and to structures, they will be directly compared. i.e. diff:"name,identifier"

• immutable : Will omit this struct field from diffing. When using diff.StructValues() these values will be added to the returned changelog. It's usecase is for when we have nothing to compare a struct to and want to show all of its relevant values.

Usage

Basic Example

Diffing a basic set of values can be accomplished using the diff functions. Any items that specify a "diff" tag using a name will be compared.

import "github.com/r3labs/diff"

type Order struct {
    ID    string `diff:"id"`
    Items []int  `diff:"items"`
}

func main() {
    a := Order{
        ID: "1234",
        Items: []int{1, 2, 3, 4},
    }

    b := Order{
        ID: "1234",
        Items: []int{1, 2, 4},
    }

    changelog, err := diff.Diff(a, b)
    ...
}

In this example, the output generated in the changelog will indicate that the third element with a value of '3' was removed from items. When marshalling the changelog to json, the output will look like:

[
    {
        "type": "delete",
        "path": ["items", "2"],
        "from": 3,
        "to": null
    }
]

Running Tests

make test

Contributing

Please read through our contributing guidelines. Included are directions for opening issues, coding standards, and notes on development.

Moreover, if your pull request contains patches or features, you must include relevant unit tests.

Versioning

For transparency into our release cycle and in striving to maintain backward compatibility, this project is maintained under the Semantic Versioning guidelines.

Copyright and License

Code and documentation copyright since 2015 r3labs.io authors.

Code released under the Mozilla Public License Version 2.0.