Field Options

Field Options are custom schema options available at field level (for fields of struct type). These options either modifies the schema or adds validations to the field on which it is applied.

mgod supports the following field options -

__id

• BSON Tag: mgoID
• Accepts Type: bool
• Default Value: true for custom type fields

It defines if _id field needs to be added in a object.

note

This option is only applicable for fields holding structs.

Example

type UserProject struct {
	Name string
}

type Metadata struct {
	TeamIDs  []string      `bson:"teamIds"`
	Projects []UserProject `mgoID:"false"`
}

type User struct {
	Name     string
	Metadata *Metadata `bson:"meta"`
}

userDoc := User{
	Name: "Gopher",
	Metadata: Metadata{
		TeamIDs: []string{"team1", "team2"},
		Projects: []UserProject{
			UserProject{Name: "Project 1"},
			UserProject{Name: "Project 2"},
		},
	},
}

user, _ := userModel.InsertOne(context.TODO(), userDoc)

Output:

{
	"_id": ObjectId("65697705d4cbed00e8aba717"),
	"name": "Gopher",
	"meta": {
		"_id": ObjectId("65697705d4cbed00e8aba718"),
		"teamIds": ["team1", "team2"],
		"projects": [
			{
				"name": "Project 1"
			},
			{
				"name": "Project 2"
			}
		]
	}
}

See how _id field is added for meta object because mgoID is true by default for struct type fields. Also, note how _id field is skipped for projects object as it was set to false explicitly in type declaration.

required

• Accepts Type: bool
• Default Value: true

It defines if a field is required or not. The option can be invalidated using omitempty property of bson tag.

Example

type User struct {
	Name   string
	Age    int32
	Height *float `bson:",omitempty"`
}

In the above type, height field is set to not required.

userDoc := User{
	Name: "Gopher",
}

The above doc will throw error because Age field is required.

userDoc := User{
	Name: "Gopher",
	Age: 18,
}

This doc will work fine.

default

• BSON Tag: mgoDefault
• Accepts Type: string
• Default Value: nil

It provides the default value for a field. The value of this option is used when the field is not present in the input document.

note

This option is applicable only for fields that are not of custom type (custom structs).

Example

type UserProject struct {
	Name string
}

type Metadata struct {
	TeamIDs  []string      `bson:"teamIds"`
	Projects *[]UserProject `mgoID:"false" mgoDefault:"[]"`
}

type User struct {
	Name     string
	Age      *int32 `mgoDefault:"18"`
	Metadata *Metadata `bson:"meta"`
}

userDoc := User{
	Name: "Gopher",
	Age: 30,
	Metadata: Metadata{
		TeamIDs: []string{"team1", "team2"},
	},
}

user, _ := userModel.InsertOne(context.TODO(), userDoc)

Output:

{
	"_id": ObjectId("65697705d4cbed00e8aba717"),
	"name": "Gopher",
	"age": 30,
	"meta": {
		"_id": ObjectId("65697705d4cbed00e8aba718"),
		"teamIds": ["team1", "team2"],
		"projects": []
	}
}

See how the value of age field was used because it was provided in the input doc and how the default value of projects field is used because it was missing from the input doc.