In short, this is a GraphQL request JSON body builder for Kotlin. It will generate the JSON string for request body that work with GraphQL Server. For example, we have this GraphQL query to list all notes:

query {
    notes {
        id
        createdDate
        content
        author {
            name
            avatarUrl(size: 100)
        }
    }
}

Which is written in Kotlin using Kraph like this:

Kraph {
    query {
        fieldObject("notes") {
            field("id")
            field("createdDate")
            field("content")
            fieldObject("author") {
                field("name")
                field("avatarUrl", mapOf("size" to 100))
            }
        }
    }
}

As you can see, we can achieve our goal with just a few tweaks from the original query.

NOTE: Kraph is still in an early stage. The usage may change in further development.

• DSL builder style. Make it easier to read and use.
• Support Cursor Connection and Input Object Mutation in Relay.

Adding Kraph to build.gradle

repositories {
    jcenter()
}

dependencies {
    compile "me.lazmaid.kraph:kraph:x.y.z"
}

If you are not familiar with GraphQL syntax, it is recommended to read the GraphQL introduction for an overview of how Graphql works. Usually, you should be able to use queries from other tools (e.g. GraphiQL) with a few tweaks. First, let's see what Kraph provides for you.

• query and mutation represents the Query and Mutation operations of GraphQL. The name of the query or mutaton can be passed as a string.

  GraphQL:

  query GetUsers {
    ...
  }

  Kraph:

  Kraph {
      query("GetUsers") {
          ...
      }
  }

  GraphQL:

  mutation UpdateUserProfile {
    ...
  }

  Kraph:

  Kraph {
      mutation("UpdateUserProfile") {
          ...
      }
  }

• field and fieldObject represent accessors for fields. Though there are technically no differences, fieldObject may be chosen for clarity to indicate that a field must contain another set of nested fields as an argument. Both of them take a Map<String, Any> that maps Kotlin data types to the GraphQL data types for input objects. You can also specify an alias using alias to change the name of the returned field.

  query {
    users {
      nick: name
      email
      avatarUrl(size: 100)
    }
  }

  Kraph {
      query {
          fieldObject("users") {
              field("name", alias = "nick")
              field("email")
              field("avatarUrl", args = mapOf("size" to 100))
          }
      }
  }

• fragment provides a mechanism for creating GraphQL Fragments. To use a fragment in a query requires two steps. The first is to define the fragment, letting Kraph know how to handle it later:

  fragment UserFragment on User {
    name
    email
    avatarUrl(size: 100)
  }

  Kraph.defineFragment("UserFragment") {
      field("name")
      field("email")
      field("avatarUrl", mapOf("size" to 100))
  }

  Then, when you are creating your query, you can simply use the fragment and its fields will be expanded:

  query {
    users {
      ...UserFragment
    }
  }

• fragment provides a mechanism for creating GraphQL Fragments. To use a fragment in a query requires two steps. The first is to define the fragment, letting Kraph know how to handle it later:

  fragment UserFragment on User {
    name
    email
    avatarUrl(size: 100)
  }

  Kraph.defineFragment("UserFragment") {
      field("name")
      field("email")
      field("avatarUrl", mapOf("size" to 100))
  }

  Then, when you are creating your query, you can simply use the fragment and its fields will be expanded:

  query {
    users {
      ...UserFragment
    }
  }

  Kraph {
      query("GetUsers") {
          fieldObject("users") {
              fragment("UserFragment")
          }
      }
  }

• func represents a Field inside a Mutation block that follows the Relay Input Object Mutations specification.

  mutation {
    userLogin(input: {email: "[email protected]", password: "abcd1234"}) {
      accessToken
      user {
        id
        email
      }
    }
  }

  Kraph {
      mutation {
          func("userLogin", input = mapOf("email" to "[email protected]", "password" to "abcd1234")) {
              field("accessToken")
              fieldObject("user") {
                  field("id")
                  field("email")
              }
          }
      }
  }

• cursorConnection represents a Field that follows the Relay Cursor Connections specification

  query {
     users(first: 10, after: "user::1234") {
      edges {
        node {
          id
          name
        }
      }
    }
  }

  Kraph {
      cursorConnection("users", first = 10, after = "user::1234") {   
          edges {
              node {
                  field("id")
                  field("name")
              }
          }
      }
  }

• toRequestString() will generate a JSON body to send in POST request.
• toGraphQueryString() will give you the formatted GraphQL string. This is very useful for debugging.

  val query = Kraph {
      query {
          fieldObject("users") {
              field("name")
              field("email")
              field("avatarUrl", args = mapOf("size" to 100))
          }
      }
  }    
  
  println(query.toRequestString())
  /*
   * Result:
   * {"query": "query {\nnotes {\nid\ncreatedDate\ncontent\nauthor {\nname\navatarUrl(size: 100)\n}\n}\n}", "variables": null, "operationName": null}
   */
  println(query.toGraphQueryString())
  /*
   * Result:
   * query {
   *   notes {
   *     id
   *     createdDate
   *     content
   *     author {
   *       name
   *       avatarUrl(size: 100)
   *     }
   *   }
   * }
   */

• requestQueryString(), requestVariableString() and requestOperationName() provide more fine grained access to the components of the full request string, which are sometimes necessary depending on your HTTP request builder and GraphQL server setup. They provide the values for the query, variables, and operationName parameters, respectively, and so are good for creating GET requests. Please note that requestVariableString() will always return null until variable support is implemented.

We use Github issues for tracking bugs and requests. Any feedback and/or PRs is welcome.