Merging Schemas

[cueckoo]

Originally opened by @rawkode in cuelang/cue#872

I have a Go application that uses Cue to validate the users YAML files. I store the Cue in Go as a hard coded string.

However, I want to allow the user to provide extensions to the schema, which I am loading into a Go variable as well.

The code looks like:

        var model = make(map[string]interface{})

        // "cue" is a Cue string 
	err := cuego.Constrain(&model, cue)
	if err != nil {
		return nil, cueutils.UsefulError(err)
	}

	bytes, err := ioutil.ReadFile(path)
	if err != nil {
		return nil, cueutils.UsefulError(err)
	}

	err = yaml.Unmarshal(bytes, &model)
	if err != nil {
		return nil, cueutils.UsefulError(err)
	}

	err = cuego.Complete(&model)
	if err != nil {
		return nil, cueutils.UsefulError(err)
	}

I'd like to be able to "merge" the cue variable with another Go string.

Examples of cue and extends:

cue := `{
  first_name: string
}`

extends := `{
  last_name: string
}`

I was really hoping cuego.Merge(cue, extends) would kind of work :)

[cueckoo]

Original reply by @mpvl in cuelang/cue#872 (comment)

Note entirely sure what your flow is, but could you not just call Constrain repeatedly for the same value?

In general CUE, not using cuego, one could use FillPath or Unify for this purpose:

// Filling multiple Go values:

var r cue.Runtime
inst, err := r.Compile("foo", "_")
// ... handle error
v := inst.Value()

root := cue.Path{}

// Merge in Go values
v = v.FillPath(root, value1)
v = v.FillPath(root, value2)

// Merge in CUE values
inst, err = r.Compile("", cueString1)
v = v.Unify(inst.Value()) // can also use FillPath(root, v).

if err := v.Err(); err != nil {
    // handle error
}

[cueckoo]

Original reply by @rawkode in cuelang/cue#872 (comment)

I did try calling Constraint twice, but it didn't function as expected.

I'll give your example code a go 👍🏼

Thanks