Using cuelang, how to put a condition on a struct field of a hint pattern generated from a Golang module

php editor Strawberry will introduce to you today how to use cuelang to place conditions on the structural fields of the prompt pattern generated from the Golang module. cuelang is a powerful language for defining and validating data structures that integrates seamlessly with Golang. When we use modules generated by Golang, we often encounter situations where we need to add conditions on structure fields. This article will explain in detail how to use cuelang to achieve this requirement, and help everyone better understand and apply the powerful functions of cuelang. Next, we will analyze this problem step by step and provide relevant sample code so that everyone can better understand it. Let’s take a look!

Question content

I would like to put additional constraints on certain structural fields in the prompt pattern generated from the Golang module.

The following schema.cue is generated from the corresponding Golang module

package app

#App: {
  version: string @go(Version)
}
...

I tried specifying the hint annotation in the source Golang module (example below), but this did not result in the correct constraints in the generated schema.cue.

type App struct {
    Version         string    `cue:"'version: =~core.myapp.dev/v1'" yaml:"Version"`
}

Another approach I tried was to use conjunctions to extend instances of the schema.

CB79515A7EDA1BA1F8290B9FA56F2A98

However, cue vet schema.cue test/badVersionValue.yaml, did not generate any errors for stdout, where badVersionValue.yaml contains Version: badstring.

I was able to get a working solution with the following manually written schema.cue

package app

version: =~"core.myapp.dev/v1"

This way cue vet schema.cuetests/badVersionValue.yaml will generate

Version: invalid value "badstring" (out of bound =~"core.myapp.dev/v1"):
...

The downside to this approach is that I would be writing the hint pattern files from scratch, rather than using and iterating over files generated from the Golang source code/source of truth.

Solution

I misunderstood how to properly use prompts for review when it comes to definitions.

Based on this example from cuetorials.com, you can specify -d where "#Schema" is located

Not only do I see the following success, where the yaml file content is Version: 5.

cue vet badVersionStr.yaml schema.cue -d '#App'                         
Version: conflicting values 5 and string (mismatched types int and string):

And also append constraints to existing fields according to the OP:

package app

#App: {
  version: string @go(Version)
  version: =~ "core.myapp.dev/v1"
}
...

Now produces the expected output

cue vet badVersionStr.yaml schema.cue -d '#App'                         
Version: invalid value "badString" (out of bound =~"core.myapp.dev/v1"):

edit: This is a better approach for people who use Golang modules for everything. You can place constraints as struct field annotations in Golang modules.

# app.go
type App struct {
   Version     string     `cue:"=~\"core.myapp.dev/v1\"" yaml:"Version"`
...

Use cue get go app.go and you will get a corresponding app_go_gen.cue which should look like this

#App: {
    Version:     string & =~"core.myapp.dev/v1" @go(Version)
...

This is valid when executing the cue vet ... command referenced above. This means that you only need to specify constraints in the Golang module and then generate a Cue schema that will interpret these annotations as constraints on the structure fields.

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