Custom Messages

Zog has multiple ways of customizing issue messages as well as support for i18n. Here is a list of the ways you can customize issue messages:

1. Using the z.Message() function

This is a function available for all tests, it allows you to set a custom message for the test.

err := z.String().Min(5, z.Message("string must be at least 5 characters long")).Parse("bad", &dest)
// err = []ZogIssue{{Message: "string must be at least 5 characters long"}}

2. Using the z.MessageFunc() function

This is a function available for all tests, it allows you to set a custom message for the test.

This function takes in an IssueFmtFunc which is the function used to format issue messages in Zog. It has the following signature:

type IssueFmtFunc = func(e *ZogIssue, ctx z.Ctx)

err := z.String().Min(5, z.MessageFunc(func(e *z.ZogIssue, ctx z.Ctx) {
	e.SetMessage("string must be at least 5 characters long")
})).Parse("bad", &dest)
// err = []ZogIssue{{Message: "string must be at least 5 characters long"}}

3. Using the WithIssueFormatter() ExecOption

This allows you to set a custom ZogIssue formatter for the entire parsing operation. Beware you must handle all ZogIssue codes & types or you may get unexpected messages.

err := z.String().Min(5).Email().Parse("zog", &dest, z.WithIssueFormatter(func(e *z.ZogIssue, ctx z.Ctx) {
	e.SetMessage("override message")
}))
// err = []ZogIssue{{Code: min_length_issue, Message: "override message"}, {Code: email_issue, Message: "override message"}}

See how our issue messages were overridden? Be careful when using this!

4. Iterate over the returned issues and create custom messages

errs := userSchema.Parse(data, &user)
msgs := FlattenZogIssues(errs)

// This is basically the implementation of the z.Issues.Flatten() method
func FlattenZogIssues(errs z.ZogIssueList) map[string][]string {
	// iterate over issues and create custom messages based on the issue code, the params and destination type
	result := make(map[string][]string)
	for _, issue := range errs {
		path := issue.PathString()
		if path == "" {
			path = "$root"
		}
		result[path] = append(result[path], issue.Message)
	}
	return result
}

5. Configure issue messages globally

Zog provides a conf package where you can override the issue messages for specific issue codes. You will have to do a little digging to be able to do this. But here is an example:

import (
	conf "github.com/Oudwins/zog/zconf"
	zconst "github.com/Oudwins/zog/zconst"
)

// override specific issue messages
// For this I recommend you import `zog/zconst` which contains zog constants but you can just use strings if you prefer
conf.DefaultIssueMessageMap[zconst.TypeString]["my_custom_issue_code"] = "my custom issue message"
conf.DefaultIssueMessageMap[zconst.TypeString][zconst.IssueCodeRequired] = "Now all required issues will get this message"

But you can also outright override the issue formatter and ignore the issues map completely:

// override the issue formatter function - CAREFUL with this you can set every issue message to the same thing!
conf.IssueFormatter = func(e *p.ZogIssue, ctx z.Ctx) {
	// do something with the issue
	...
	// fallback to the default issue formatter
	conf.DefaultIssueFormatter(e, p) // this uses the DefaultErrMsgMap to format the issue messages
}

6. Use the i18n package

Really this only makes sense if you are doing i18n. Please please check out the i18n section for more information.

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