Parsing

What is parsing?

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...

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:

• Global Coercion - Change the default coercion behaviour for all schemas. More details on this in the configuration page.
• Per schema coercers - Define custom coercion functions for your schemas.

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 Context

Zog uses a ParseCtx to pass around information related to a specific schema.Parse() call. Currently use of the parse context is quite limited but it will be expanded upon in the future. It can be used for the following:

Pass custom data to functions

Here is an example with a pretransform

nameSchema := z.String().Min(3).PreTransform(func(data any, ctx z.ParseCtx) (any, error) {
  char := ctx.Get("split_by")
  return strings.Split(data.(string), char), nil
})
nameSchema.Parse("Michael Jackson", &dest, z.WithCtxValue("split_by", " "))

Change the error formatter for this execution

This might be useful for localization, or for changing the error messages for one specific execution.

nameSchema := z.String().Min(3)
nameSchema.Parse(data, &dest, z.WithErrFormatter(MyCustomErrorMessageFormatter))

Parsing Execution Structure

1. Pretransforms
   • On error all parsing and validation stops and error is returned.
   • Can be caught by catch
2. Default Check -> Assigns default value if the value is nil value
3. Optional Check -> Stops validation if the value is nil value
4. Casting -> Attempts to cast the value to the correct type
   • On error all parsing and validation stops and error is returned
   • Can be caught by catch
5. Required check ->
   • On error: aborts if the value is its nil value and returns required error.
   • Can be caught by catch
6. Tests -> Run all tests on the value (including required)
   • On error: validation errors are added to the errors. All validation functions are run even if one of them fails.
   • Can be caught by catch
7. PostTransforms -> Run all postTransforms on the value.
   • On error you return: aborts and adds your error to the list of errors
   • Only run on valid values. Won't run if an error was created before the postTransforms