Expanding a product when retrieving a plan causes JSON unmarshalling errors

[majelbstoat]

Simple repro:

		p, err := plan.Get(code, &stripe.PlanParams{
			Params: stripe.Params{
				Expand: []*string{stripe.String("product")},
			},
		})
		if err != nil {
			log.Fatal(err)
		}

Expected outcome is that a plan is returned. Actual behaviour is:

2018/09/11 15:23:28 json: cannot unmarshal object into Go struct field Plan.product of type string

The following also fails for the same reason.

		params := &stripe.PlanParams{}
		params.AddExpand("product")
		p, err := plan.Get(code, params)

Current workaround is to just make a second request, but that's kind of wasteful.

I'd submit a PR, but I'm not sure what your preferred approach to supporting both string and expanded return types is.

[majelbstoat]

(The Java SDK has Product for the string, and ProductObject for the object, which is kind of ugly, but works.)

[majelbstoat]

Ah, I think it's missing an UnMarshalJSON method. I'll take a crack at it.

[remi-stripe]

@majelbstoat Nice catch and sorry about the trouble. The solution is to replace the string by a *Product and it will "just work".

[majelbstoat]

ooh, neat.

[majelbstoat]

wait, no, I don't actually understand 😂. Expand takes a slice of string pointers: []*string. stripe.String() takes a string. I don't see anything that will take a Product pointer for expansion 😬. Can you show a quick example?

[remi-stripe]

@majelbstoat Sorry I could have been clearer! This line says:

	Product         string              `json:"product"`

This means that when you deserialize a plan we expect Product to be a string. But if you expand it it will be a hash. So instead you should have this line:

	Product         *Product              `json:"product"`

This will let stripe-go deserialize the product properly. If a string is returned we will automatically set Product.Id to the string value. If it's a hash we will deserialize the product automatically.

This works because the Product struct has a custom UnmarshalJSON here which will deserialize the resource based on whether it's a string or a hash.