Revel parameter validation

Revel brings its own parameter validation:

• Provides a validation context for collecting and managing validation errors (via key and message).
• Auxiliary functions are used to examine data and bring error messages into context.
• A template function that gets error information from the validation context through key.

The sample application provides some examples of in-depth understanding of parameter validation.

Inline error message

The following demonstrates using inline error messages to validate fields

func (c MyApp) SaveUser(username string) revel.Result {
    // Username (required) 至少 4 - 15 个字符.
    c.Validation.Required(username)
    c.Validation.MaxSize(username, 15)
    c.Validation.MinSize(username, 4)
    c.Validation.Match(username, regexp.MustCompile("^\\w*$"))

    if c.Validation.HasErrors() {
        // 在flash上下文中保存验证错误并重定向
        c.Validation.Keep()
        c.FlashParams()
        return c.Redirect(Hotels.Settings)
    }

    // All the data checked out!
    ...
}

1. username field validation conditions (Required required, MinSize minimum length, MaxSize maximum length, Match matches a regular expression).
2. Each validation condition returns a ValidationResult, and if the validation does not pass, the validation results are saved to the validation context.
3. As part of building the application, Revel records the name of the validated variable and uses it as the default key in the validation context (after which you can get the validation error message through key).
4. Validation.HasErrors() true if validation does not pass
5. Validation.Keep() Revel serialization to verify the error message into the Flash cookie.
6. Revel redirects to Hotels.Settings method.

The Hotels.Settings method renders a template:

{{/* app/views/Hotels/Settings.html */}}
...
{{if .errors}}Please fix errors marked below!{{end}}
...
<p class="{{if .errors.username}}error{{end}}">
    Username:
    <input name="username" value="{{.flash.username}}"/>
    <span class="error">{{.errors.username.Message}}</span>
</p>

It does three things:

1. Check the error field in the errors map username
2. Bring username
3. An error message is displayed below input (if no error message is specified after an error in the validation field, the default error message for the validation function is displayed)

Note: The template function field uses a validation error framework to make it easier to write templates.

The error message for the top

If the error messages are displayed in one place, the template becomes simple (for example, in a red box at the top of the page.)

The following example is two different from the one above:

1. Instead of using the validation function's default error Message specified a validation error message for the field
2. We print all the error messages at the top of the page

The code is as follows:

func (c MyApp) SaveUser(username string) revel.Result {
    // Username (必填) 至少 4 - 15 字符.
    c.Validation.Required(username).Message("Please enter a username")
    c.Validation.MaxSize(username, 15).Message("Username must be at most 15 characters long")
    c.Validation.MinSize(username, 4).Message("Username must be at least 4 characters long")
    c.Validation.Match(username, regexp.MustCompile("^\\w*$")).Message("Username must be all letters")

    if c.Validation.HasErrors() {
        // 保存错误信息到 flash 上下文中并重定向
        c.Validation.Keep()
        c.FlashParams()
        return c.Redirect(Hotels.Settings)
    }

    // All the data checked out!
    ...
}

The template is as follows:

{{/* app/views/Hotels/Settings.html */}}
...
{{if .errors}}
<div class="error">
    <ul>
    {{range .errors}}
        <li> {{.Message}}</li>
    {{end}}
    </ul>
</div>
{{end}}
...