Validation

goodm validates models automatically on Create and Update. Validation runs after hooks and before the database write.

Validation Rules

Required

Fields tagged required must be non-zero. Go's zero values are: "" for strings, 0 for ints, false for bools, zero bson.ObjectID, zero time.Time.

Name string `bson:"name" goodm:"required"`

Enum

Fields tagged enum=a|b|c must contain one of the listed values (pipe-separated). Only validated when the field is non-zero.

Status string `bson:"status" goodm:"enum=draft|published|archived"`

Min / Max

Numeric fields tagged min=N or max=N are bounded. Only validated when non-zero.

Age   int `bson:"age"   goodm:"min=13,max=120"`
Price int `bson:"price" goodm:"min=0"`

Immutable

Fields tagged immutable cannot change after creation. On Update, goodm fetches the existing document and compares each immutable field using reflect.DeepEqual.

Username string `bson:"username" goodm:"required,immutable"`

ValidationErrors

When validation fails, a ValidationErrors (slice of ValidationError) is returned:

err := goodm.Create(ctx, user)

var ve goodm.ValidationErrors
if errors.As(err, &ve) {
    for _, e := range ve {
        fmt.Printf("%s: %s\n", e.Field, e.Message)
        // e.Field is the bson field name (e.g. "email")
        // e.Message describes the violation
    }
}

Example messages: - "field is required" - "value \"xyz\" is not in enum [draft published archived]" - "value 5 is less than minimum 13" - "value 200 exceeds maximum 120" - "field is immutable and cannot be changed"

Subdocument Validation

Validation recurses into nested structs and slice elements. Error paths use dot notation for nested fields and bracket notation for slice indexes:

order := &Order{
    Name: "Order1",
    Address: Address{Street: ""}, // required — will fail
    Items: []OrderItem{
        {Name: "", Quantity: 2}, // required — will fail
    },
}
err := goodm.Create(ctx, order)

// Errors:
// - Field: "address.street", Message: "field is required"
// - Field: "address.city",   Message: "field is required"
// - Field: "items[0].name",  Message: "field is required"

Path format examples: - address.street — nested struct field - items[0].name — first element of a slice - shipping.address.city — deeply nested (subdoc within subdoc)

Nil pointer subdocuments are skipped during inner validation (the field-level required check catches their absence). Empty slices produce no inner validation errors.

When Validation Runs

Operation	Validates?	Immutable Check?
Create	Yes	No (no prior state)
CreateMany	Yes (per model)	No
Update	Yes	Yes (fetches existing doc)
UpdateOne	No	No
UpdateMany	No	No

Manual Validation

You can validate a model without performing a database operation:

schema, _ := goodm.Get("User")
errs := goodm.Validate(user, schema)
if len(errs) > 0 {
    // handle validation errors
}