Common library for Go

The library provides commonly used features for Go language.

Features

Convert between map and struct

General sample

...

import "github.com/easeway/langx.go/mapper"

...

type Person struct {
    Name    string `json:"name"`
    Address string `json:"address"`
    Age     int `json:"age"`
    Emails  []string `json:"emails"`
}

var JSONString = `{"name": "Brainer", "address": ...}`
func main() {
    map0 := make(map[string]interface{})
    err := json.Unmarshal([]byte(JSONString), map0)
    m := &mapper.Mapper{}
    var person Person
    m.Map(&person, map0)
    ...
    map1 := make(map[string]interface{})
    m.Map(map1, &person)
    json.Marshal(map1)
    ...
}

Anonymous structure

If the structure contains anonymous structures, the fields are treated as the same level.

type Person struct {
    Name    string `json:"name"`
    Address string `json:"address"`
}

type User struct {
    Person
    Roles string `json:"roles"`
}

var JSONString = `{"name": "Brainer", "address": ..., "roles": ["admin", "dev"]}`
...

Squash structure

For non-anonymous structure, flatten the fields, and achieve the same effect as anonymous structure.

type Person struct {
    Name    string `json:"name"`
    Address string `json:"address"`
}

type User struct {
    Person Person `json:",squash"`
    Roles  string `json:"roles"`
}

var JSONString = `{"name": "Brainer", "address": ..., "roles": ["admin", "dev"]}`
...

Multi-mapping

If a value in JSON can be of different types, multi-mapping solve the problem.

With the following JSON documents:

{ "additionalProperties": true }

{ "additionalProperties": ["alias", "age"] }

The structure can be defined as:

type MultiMapping struct {
    AllowAdditionalProperties bool     `json:"additionalProperties,omitempty"`
    AdditionalProperties      []string `json:"additionalProperties,omitempty"`
}

Please note, omitempty is recommended. Otherwise Mapper gets confused when converting the structure to map.

Wildcard mapping

In most cases, a map can be converted into a structure. However, in some cases, the value can be a map, or some other values. wildcard fields are used to accept non-map values.

type Command struct {
    Shell string `json:"*"`
    Macro string `json:"macro"`
}

type Target struct {
    Commands []*Command `json:"commands"`
}

The definition above can accept the following documents:

{
    "commands": [
        { "macro": "wait" },
        ...
    ]
}

Or

{
    "commands": [
        "mkdir -p /tmp/abc",
        "cp ...",
        {"macro": "wait"},
        ...
    ]
}

When the item in commands is a simple string, it doesn't match the expected type *Command, as Command has a wildcard field of type string, the value is filled in.

It's very useful when the schema has a few fix properties and also open to additional properties. The following structure is usually defined for this case:

type OpenStruct struct {
    Type       string                 `json:"type"`
    Properties map[string]interface{} `json:"*"`
}

Currently, structures with wildcard fields can't be converted back to a map.

Override the tag name

It's not necessary to require json as tag name in struct fields. Construct a Mapper with a list of tag names is possible:

m := &Mapper{FieldTags: []string{"n", "map"}}

It will search for tags in the order of n, map until a tag is found.

Trace the mapping

This is mostly for debugging purpose. Assign a function to Mapper.Tracer can track the traversal during conversion.

Aggregated Errors

Sometime multiple errors need aggregated and reported as a single error. The type AggregatedError implements this behavior.

import "github.com/easeway/langx.go/errors"

...
// First define an AggregatedError
errs := errors.AggregatedError{}
...
errs.Add(err)
// Or
errs.AddErr(err)
// Or
errs.AddMany(err1, err2, ...)
// Or if the function only returns error
errs.Add(os.Remove(...))
// And finally return
return errs.Aggregate()

When using Add/AddErr/AddMany, don't worry about err is nil or not, nil won't be added. And Aggregate only returns nil if no error is added.

License

MIT