02.hotchocolate-intro.md

Hotchocolate GraphQL

The project uses the library Hotchocolate as GraphQL server implementation. It is not the only .Net implementation of a GraphQL server, but its ease and power are remarkable and the performances are much better than the Microsoft version.

Banana Cake Pop

Let's begin to explore the scheme made.

To do this it is possible to begin to discover some of the tools of the GraphQL ecosystem, eg. Banana Cake Pop, which is incorporated in the HotChocolate library and made available at startup with the line:

app.UseEndpoints(endpoints =>
{
    endpoints.MapGraphQL();
});

which allows you to access Banana Cake Pop via the /graphql route. BCP allows you to query our graphQL server.

Query Language

"QL" in GraphQL obviously stands for Query Language and this is another relevant feature of this technology, in fact it allows you to manage in a declarative way even complex logics such as filters, variables or code reuse through fragment.

Arguments

In the following query you can see how to extend our types by allowing our query methods to handle arguments

query editori {
    publishers(skip:0, limit: 10) {
      id
      name
    }
}

query autori {
    authors(limit: 5) {
      id
      firstName
      surnName
    }
}

query autore {
    a1: authorById(id: "2d2cbbee-5a3a-4102-bc41-04679bfa2968") {
      firstName
      surnName
      webSite
      email
    }

    a2: authorById(id: "520163be-6122-47d3-91a4-56a203a5c2aa") {
      firstName
      surnName
      webSite
      email
    }    
}

Variables, directives e fragments

There are different types of directives including:

• @include(if: Boolean)
• @skip(if: Boolean)

used in the following query:

query autoriFragment($limit: Int, $shouldInclude: Boolean!) {
    authors(limit: $limit) @include(if:$shouldInclude) {
      ... Autore
    }
}

fragment Autore on Author {
  id
  firstName
  surnName
}

There are two types of fragments: fragment (as in the example above) which allow you to reuse the same block of information returned between different queries and inline fragment which allow you to manage fragments directly in queries:

query autoriFragment($limit: Int, $shouldInclude: Boolean!) {
    authors(limit: $limit) @include(if:$shouldInclude) {
      ... on Author {
          id
          firstName
          surnName
      }
    }
}

This second mode is very useful when a query can return different kinds of types (very useful implementing Global Object Identification, as we will see later).