Building a .NET GraphQL Server

GraphQL is a query language developed by Facebook in 2012 (publicly released in 2015). In a GraphQL query, the consumer of an API specifies the structure of the data it needs. The server executes the query, collects the data from one or various data sources, filters out the fields which aren’t specified in the query, and returns the result as JSON objects.

What problem does GraphQL solve?

Imagine this Rest API. It has two endpoints:

[GET] /room
returns: 
[
  { 
    roomId: 1, 
    locationId: 1, 
    name: 'Ideation Zone', 
    capacity: 30 
  }, 
  { 
    roomId: 2, 
    locationId: 1, 
    name: 'Creative Arena', 
    capacity: 60 
  }
]

And

[GET] /presentation
returns
[
  {  
    presentationId: 1,
    presentorIds: [5, 24],    
    roomId: 1,
    start: '2022-10-02T13:00:00Z',
    end: '2022-10-02T15:00:00Z',
    title: 'GraphQL for newbies',
    description: 'Lorum ipsum...'
  },
  { 
    presentationId: 2,
    presentorIds: [6],    
    roomId: 2,
    start: '2022-10-02T14:00:00Z',
    end: '2022-10-02T15:00:00Z',
    title: 'Advanced Rest',
    description: 'Dolar sit amet..'
  }
]

Usually, the product owner asks the team to build the following table:

| Presentation        | Starts at        | Room           |
+---------------------+------------------+----------------+
|…