Cookbooks #1542
Cookbooks #1542
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akhesaCaro
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| structure. We only deal with non-nested APIs in which every endpoint is on the same | ||
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| If a you need nesting because you have different branches in your API tree, you |
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| # Record-based APIs: the nested records case | |||
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nested API*
It does indeed result in "nested records", but this merely mirrors the structure of the API, which is the central element that should be in the title IMO
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| *Available in Servant 0.19 or higher* | ||
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| Servant offers a very natural way of constructing APIs with nested records, called `NamedRoutes`. |
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Do you think it'd be good to clarify what "nested" means here? Describing the general pattern dividing up APIs in sub-APIs and being able to combine those easily, etc.
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Generic cookbook should have clarified this beforehand.
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| Finally, we can run the server and connect the API routes to the handlers as usual: | ||
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| ``` haskell |
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don't we want to use genericServe here? to stay in the "record world".
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There's no need as NamedRoutes has a HasServer instance. So no need to specialised functions that call toServant and fromServant
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I really don't see the point of introducing genericServe here — it makes the overall story less uniform.
We checked yesterday, and genericServe produces the exact same error message as serve if Generic instances are missing (a relatively unhelpful message mentioning Generic) so we are not gaining anything.
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Well that forces people to use NamedRoutes at the top, which is completely unnecessary if your entire API is made of records. The most direct way to serve a record of handlers is genericServe, hence my suggestion.
It'd be good to have some place that really explains those ":<|> separated" and "record" worlds and how we can go from one to the other, at all levels. But in the meantime, in the interest of giving the simplest code possible in the cookbook, without having to explain that named routes is an "adaptator" of sorts to plug records into old-style APIs, I'd recommend personally recommend genericServe (but do as you wish, this is just my opinion).
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I think:
serveGeneric (Proxy @MyApi) myServerisn't so much shorter than:
serve (Proxy @(NamedRoutes MyAPI)) myServeras to warrant the introduction of another function in the cookbook. It gives off the feeling that record APIs still somewhat live in a different world — which they now don't.
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That function is already introduced in the introductory cookbook: https://docs.servant.dev/en/stable/cookbook/generic/Generic.html#server
(and even the ServerT version)
And requires appending a few chars to serve vs another pair of parens and the NamedRoutes thing.
But I also suggested to @akhesaCaro at some point that another possibility could just be to pick one and show the equivalent with the other, in a commented-out (or not, could just be with a different name) line right below.
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| ``` haskell | ||
| movieCatalogClient :: API (AsClientT ClientM) | ||
| movieCatalogClient = client api -- remember: api :: Proxy MovieCatalogAPI |
| , delete = deleteMovieHandler movieId | ||
| } | ||
| ``` | ||
| As you might have noticed, we build our handlers out of the same record types we used to define our API: `MoviesAPI` and `MovieAPI`. What kind of magic is this ? |
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Might fit well in the generic cookbook? Where we introduce the whole record-API machinery.
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The two cookbooks should IMHO be merged into a single cookbook, the non-nested / flat API case being the first section, and the nested records one expanding upon the first. So we can move this section a bit up when we do so ; for now I think it is better if the NamedRoutes cookbook remains standalone.
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That is what I have advocated in favor of as well :-) And even putting the resulting thing in the tutorial. But in the interest of splitting that up into a bunch of much smaller steps, we're first consolidating the named routes one to make it stand as a nice follow up to the generic cookbook. Then slowly but surely proceeding with the rest of the plan.
for now I think it is better if the NamedRoutes cookbook remains standalone
We'd end up with 2 cookbooks which half-explain the same basics, before covering simple APIs and nested APIs respectively. Might not be the best option for users, no?
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| If you are interested in further understanding the built-in Servant combinators, see [Structuring APIs](../structuring-apis/StructuringApis.html). | ||
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| Since `NamedRoutes` is based on the Generic mechanism, you might want to have a look at [Sandy Maguire’s _Thinking with Types_ book](https://doku.pub/download/sandy-maguire-thinking-with-typesz-liborgpdf-4lo5ne7kdj0x). |
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Not nice to put a piracy link. Better link the official website: https://thinkingwithtypes.com/
Introducing NamedRoutes Cookbook (following #1538)
As requested by @alp,
We tried to tu put some consistency between the Generic Cookbook and this one.
The idea is to change a minimum of other cookbook as a first step.
The second step (in another PR) will be a thorough restructuration of the cookbooks.