How to add fluent model behavior¶

Objective¶

Add domain-oriented, chainable behavior without editing generated files.

Add the method to the handwritten model file¶

package content

import "strings"

func (u *User) Suspend(reason string) *User {
    reason = strings.TrimSpace(reason)
    if reason == "" {
        return u.setFieldError(
            UserFieldSuspensionReason,
            ErrSuspensionReasonRequired,
        )
    }

    u.clearFieldError(UserFieldSuspensionReason)

    return u.
        SetActive(false).
        SetSuspensionReason(reason)
}

Preserve the fluent contract¶

Use a pointer receiver and return the model pointer:

func (u *User) Rename(name string) *User

This supports:

err := user.
    Rename("Marcos Aurelio").
    Activate().
    Save(ctx)

Keep I/O at terminal methods¶

A fluent method may normalize input, validate values, update fields, mark dirty state, clear field errors, invalidate local relation caches, and compose other nonterminal methods.

It must not call Save, open a transaction, execute an sqlc query, trigger a lazy relation load, or switch sessions.

Prefer intent methods over raw setters in application code¶

Generated setters provide mechanical mutation:

user.SetActive(false)

Handwritten methods communicate business intent:

user.Suspend("manual review")

Both are valid. The domain-oriented method should normally compose generated setters so dirty tracking remains centralized.

Preserve correction semantics¶

When a method validates a field, clear the previous field error after a valid value is accepted. An append-only error list would leave the model permanently invalid after one failed attempt.