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Parsing

What is schema.Parse()?

To validate and parse your data into a destination pointer you can use the schema.Parse() function. The function signature looks like this:

schema.Parse(data, &dest, options...)

This works with any Zog Schema:

// string
var dest string
z.String().Min(3).Parse("test", &dest)
// structs
var dest User
z.Struct(z.Schema{"name": z.String().Min(3)}).Parse(map[string]any{"name": "test"}, &dest)

Under the hood Zog follows the Parsing Execution Structure and does a bunch of things under the hood to make sure your data is parsed correctly. Such as checking for zero values, coercing types, etc...

Parsing Struct Tags

By default zog will use the schema field name as the key for the parsed value. For example:

type User struct {
Name string `zog:"name"`
}

z.Struct(z.Schema{"name": z.String()}).Parse(map[string]any{"name": "test"}, &User{}) // note zog will fetch the value as map[name]

type User struct {
Name string `zog:"name"`
}

z.Struct(z.Schema{"Name": z.String()}).Parse(map[string]any{"name": "test"}, &User{}) // note zog will fetch the value as map[Name]

However, this is not always practical. For example, you may have data coming in in kebab case and you want to parse it into camel case. For this Zog supports a few struct tags:

  • json tag which works for JSON input data
  • form tag which works for form input data
  • query tag which works for query string input data
  • env tag which works for environment variables see zenv for more info
  • zog a catch all tag which works for any input data

The priority of keys is as follows: json || form || query || env -> zog -> schema field name

You can mix and match without issue:

type User struct {
Name string `zog:"first-name"`
LastName string `query:"last_name" json:"last-name"`
}

z.Struct(z.Schema{"name": z.String(), "lastName": z.String()}).Parse(map[string]any{"first-name": "test", "lastName": "Doe"}, &User{})

Coercion

Zog will attempt to coerce the data into the correct type. For example if you have a z.Int() schema and you pass in a "1" it will be coerced into an int type. This behaviour, like almost everything else in Zog, can be customized. Zog provides two main ways to customize coercion:

Per schema coercers

You can define custom coercion functions for your schemas by using the z.WithCoercer() schema option.

z.String(z.WithCoercer(func(data any) (any, error) {
return "test", nil // now the result will be "test" no matter the input
})).Parse("abc", &dest) // dest will be "test"

Parsing Execution Structure

Parsing execution structure is quite simple. It just does roughly this:

  1. Check for nil value
    • If nil take into account if schema has default value or is required
  2. Coerce value to the correct type otherwise
  3. Run validation loop
    • If a test fails, an issue is added
    • If you return an error from a transform, the execution stops and that error is returned.
    • If catch is active any error triggers it and stops the execution.

Zog Schema Parsign Execution Structure