A GraphQL library for .NET. Compiles queries into .NET Expressions (LinqProvider) for runtime execution against object graphs. E.g. against an ORM data model (EntityFramework or others) or just an in-memory object.
EntityGraphQL is a .NET library that allows you to easily build a GraphQL API on top of your data model with the extensibility to easily bring multiple data sources together in the single GraphQL schema.
EntityGraphQL builds a GraphQL schema that maps to .NET objects. It provides the functionality to parse a GraphQL query document and execute that against your mapped objects. These objects can be an Entity Framework DbContext or any other .NET object, it doesn't matter.
A core feature of EntityGraphQL with Entity Framework (although EF is not a requirement) is that it builds selections of only the fields requested in the GraphQL query which means Entity Framework is not returning all columns from a table. This is done with the LINQ projection operator Select() hence it works across any object tree.
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However the core EntityGraphQL package has no ASP.NET dependency.
Quick Start with Entity Framework
Note: There is no dependency on EF. Queries are compiled to IQueryable or IEnumberable linq expressions. EF is not a requirement - any ORM working with LinqProvider or an in-memory object will work - although EF well is tested.
1. Define your data context (in this example an EF context)
public class DemoContext : DbContext {
public DbSet<Property> Properties { get; set; }
public DbSet<PropertyType> PropertyTypes { get; set; }
public DbSet<Location> Locations { get; set; }
}
public class Property {
public uint Id { get; set; }
public string Name { get; set; }
public PropertyType Type { get; set; }
public Location Location { get; set; }
}
public class PropertyType {
public uint Id { get; set; }
public string Name { get; set; }
public decimal Premium { get; set; }
}
public class Location {
public uint Id { get; set; }
public string Name { get; set; }
}
2. Create a route
Here is an example for a ASP.NET. You will also need to install EntityGraphQL.AspNet to use MapGraphQL. You can also build you own endpoint, see docs.
public class Startup {
public void ConfigureServices(IServiceCollection services)
{
services.AddDbContext<DemoContext>(opt => opt.UseInMemoryDatabase());
// This registers a SchemaProvider<DemoContext>
services.AddGraphQLSchema<DemoContext>();
}
public void Configure(IApplicationBuilder app, DemoContext db)
{
app.UseRouting();
app.UseEndpoints(endpoints =>
{
// default to /graphql endpoint
endpoints.MapGraphQL<DemoContext>();
});
}
}
This sets up 1 end point:
POST at /graphql where the body of the post is a GraphQL query
You can authorize that route how you would any ASP.NET route. See Authorization below for details on having parts of the schema requiring Authorization/Claims
Note - As of version 1.1+ the EntityGraphQL.AspNet extension helper uses System.Text.Json. Previous versions used JSON.NET.
3. Build awesome applications
You can now make a request to your API. For example
POST localhost:5000/graphql
{
properties { id name }
}
Will return the following result.
{
"data": {
"properties": [
{
"id": 11,
"name": "My Beach Pad"
},
{
"id": 12,
"name": "My Other Beach Pad"
}
]
}
}
Lets say you have a screen in your application listing properties that can be configured per customer or user to only show exactly what they are interested in. Instead of having a bunch of checkboxes and complex radio buttons etc. you can allow a simple EQL statement to configure the results shown. Or use those UI components to build the query.
// This might be a configured EQL statement for filtering the results. It has a context of Property
(type.id = 2) or (type.id = 3) and type.name = "Farm"
This would compile to (Property p) => (p.Type.Id == 2 || p.Type.Id == 3) && p.Type.Name == "Farm";
This can then be used in various Linq functions either in memory or against an ORM.
// we create a schema provider to compile the statement against our Property type
var schemaProvider = SchemaBuilder.FromObject<Property>();
var compiledResult = EntityQueryCompiler.Compile(myConfigurationEqlStatement, schemaProvider);
// you get your list of Properties from you DB
var thingsToShow = myProperties.Where(compiledResult.LambdaExpression);
Another example is you want a customised calculated field. You can execute a compiled result passing in an instance of the context type.
// You'd take this from some configuration
var eql = @"if location.name = ""Mars"" then (cost + 5) * type.premium else (cost * type.premium) / 3"
var compiledResult = EntityQueryCompiler.Compile(eql, schemaProvider);
var theRealPrice = compiledResult.Execute<decimal>(myPropertyInstance);
