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Sample: Build web APIs with OData support using ASP.NET Core

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By FIVIL and Rick Anderson

This sample:

  • Demonstrates how to add OData query options support in an ASP.NET Core Web API app.
  • Uses the completed to-do Web API as a starting point.
  • Does not use an Entity Data Model (EDM).

Warning

A malicious or naive client may construct a query that consumes excessive resources. Such a query can disrupt access to your service. Review Security Guidance for ASP.NET Core Web API OData before starting this tutorial.

Register OData

Add the Microsoft.AspNetCore.OData NuGet package to the project.

Update the ConfigureServices method in Startup.cs with the following highlighted code:

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<TodoContext>(opt =>
        opt.UseInMemoryDatabase("TodoList"));
    services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    // requires using Microsoft.AspNet.OData.Extensions;
    services.AddOData();
}

The preceding code registers the OData service in the dependency injection (DI) container.

Configure middleware

OData can perform sorting, filtering, querying related data, and more. Each of these capabilities can be enabled or disabled with middleware.

Update Configure with the following highlighted code:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        // The default HSTS value is 30 days. You may want to change this for 
        // production scenarios, see https://aka.ms/aspnetcore-hsts.
        app.UseHsts();
    }

    app.UseDefaultFiles();
    app.UseStaticFiles();
    app.UseHttpsRedirection();
    app.UseMvc(routeBuilder =>
    {
        routeBuilder.EnableDependencyInjection();
        routeBuilder.Select().OrderBy().Filter();
    });
}

The preceding code:

  • Enables an override to the existing endpoints through DI to route builder, instead of exposing a traditional OData endpoint.
  • Enables select, order by, and filtering to the route builder.

Update the controller

Add [EnableQuery()] to the public ActionResult<IQueryable<TodoItem>> GetTodoItems() method in the TodoController:

// GET: api/Todo
[EnableQuery()]  // requires using Microsoft.AspNet.OData;
[HttpGet]
public ActionResult<IQueryable<TodoItem>> GetTodoItems()
{
    return _context.TodoItems;
}

Returning System.Linq.IQueryable or ActionResult<IQueryable> enables OData to translate queries to SQL queries using ef core capabilities. Returning other types such as IEnumerable causes OData to perform queries in the app.

Query resources using OData

Post some data to the web API app, using a tool such as HTTP REPL or Postman.

Send 5 Post requests to https://localhost:5001/api/todo with the 5 items below separately in the request body.

{
    "name": "test OData",
    "isComplete": false,
    "Type": "work",
    "priority": 1,
    "DueDate": "2019-04-18 00:00:01"
}

{
    "name": "test 2",
    "isComplete": true,
    "Type": "shopping",
    "priority": 2,
    "DueDate": "2019-04-18 08:00:01"
}

{
    "name": "test 3",
    "isComplete": true,
    "Type": "work",
    "priority": 1,
    "DueDate": "2019-04-18 09:00:01"
}

{
    "name": "test 4",
    "isComplete": false,
    "Type": "shopping",
    "priority": 3,
    "DueDate": "2019-04-18 12:00:01"
}

{
    "name": "test 5",
    "isComplete": false,
    "Type": "work",
    "priority": 2,
    "DueDate": "2019-04-18 15:00:01"
}

Send a Get request to verify the previous data has been saved. For example, http://localhost:5001/api/todo?$select=name,isComplete.

$select

The $select option specifies a subset of properties to include in the response body. For example, to get only the name and isComplete of each item, add ?$select=name,isComplete at the end the request path.

The preceding request returns the following data:

[
    {
        "Name": "Item1",
        "IsComplete": false
    },
    {
        "Name": "test 5",
        "IsComplete": false
    },
    {
        "Name": "test OData",
        "IsComplete": false
    },
    {
        "Name": "test 2",
        "IsComplete": true
    },
    {
        "Name": "test 3",
        "IsComplete": true
    },
    {
        "Name": "test 4",
        "IsComplete": false
    }
]

$orderBy

The $orderBy option can consume excessive resources. Consider using [Queryable(AllowedQueryOptions=AllowedQueryOptions.{Option})] to disable $orderBy. See Security Guidance for ASP.NET Core Web API OData for more information.

$orderBy sorts data based on one or more properties. For example, to order the data based on priority of each item, append ?$orderBy=priority to the request. For example, http://localhost:5001/api/todo?$orderBy=priority.

The preceding request returns the following data:

[
    {
        "id": 1,
        "name": "Item1",
        "isComplete": false,
        "type": null,
        "priority": 0,
        "dueDate": "0001-01-01T00:00:00"
    },
    {
        "id": 3,
        "name": "test OData",
        "isComplete": false,
        "type": "work",
        "priority": 1,
        "dueDate": "2019-04-18T00:00:01"
    },
    {
        "id": 5,
        "name": "test 3",
        "isComplete": true,
        "type": "work",
        "priority": 1,
        "dueDate": "2019-04-18T09:00:01"
    },
    {
        "id": 2,
        "name": "test 5",
        "isComplete": false,
        "type": "work",
        "priority": 2,
        "dueDate": "2019-04-18T15:00:01"
    },
    {
        "id": 4,
        "name": "test 2",
        "isComplete": true,
        "type": "shopping",
        "priority": 2,
        "dueDate": "2019-04-18T08:00:01"
    },
    {
        "id": 6,
        "name": "test 4",
        "isComplete": false,
        "type": "shopping",
        "priority": 3,
        "dueDate": "2019-04-18T12:00:01"
    }
]

Data can be sorted data based on multiple properties. For example, ?$orderBy=type,priority desc" sorts items based on type and then on priority in descending order.

$filter

The $filter option can consume excessive resources. Consider using [Queryable(AllowedQueryOptions=AllowedQueryOptions.{Option})] to disable $filter. See Security Guidance for ASP.NET Core Web API OData for more information.

$filter filters data based on a boolean condition. For example, to get only the items with priority greater than 1, append ?$filter=priority gt 1 to the request path.

The preceding request returns the following data:

[
    {
        "id": 2,
        "name": "test 5",
        "isComplete": false,
        "type": "work",
        "priority": 2,
        "dueDate": "2019-04-18T15:00:01"
    },
    {
        "id": 4,
        "name": "test 2",
        "isComplete": true,
        "type": "shopping",
        "priority": 2,
        "dueDate": "2019-04-18T08:00:01"
    },
    {
        "id": 6,
        "name": "test 4",
        "isComplete": false,
        "type": "shopping",
        "priority": 3,
        "dueDate": "2019-04-18T12:00:01"
    }
]

The following Boolean conditions can be used with the OData $filter:

Condition Description Example
eq Equals to $filter=priority eq 1
ne Not equals to $filter=priority ne 1
gt Greater than $filter=priority gt 1
ge Greater than or equal $filter=priority ge 1
lt Less than $filter=priority lt 1
le Less than or equal $filter=priority le 1
and Logical and $filter=priority gt 1 and priority lt 10
or Logical or $filter=priority gt 1 or priority lt 10
not Logical negation $filter=not endswith(name,'task')

String functions can be used with OData $filter. For more information, see the OData URI Conventions' $filter section.

$skip

$skip skips the specified records. For example, to skip first 4 items, append ?$skip=4 to the request.

The preceding request returns the following data:

[
    {
        "id": 5,
        "name": "test 3",
        "isComplete": true,
        "type": "work",
        "priority": 1,
        "dueDate": "2019-04-18T09:00:01"
    },
    {
        "id": 6,
        "name": "test 4",
        "isComplete": false,
        "type": "shopping",
        "priority": 3,
        "dueDate": "2019-04-18T12:00:01"
    }
]

Chained queries

Chained queries can consume excessive resources. Consider using [Queryable(AllowedQueryOptions=AllowedQueryOptions.{Option})] to disable expensive operations. Consider restricting $orderby to properties in a clustered index. See Security Guidance for ASP.NET Core Web API OData for more information.

OData queries can be chained to make a complex query. For example, appending ?$skip=2&$select=name,priority&$orderBy=priority desc&filter=priority gt 1 returns the following data:

[
    {
        "Name": "test 2",
        "priority": 2
    },
    {
        "Name": "test OData",
        "priority": 1
    },
    {
        "Name": "test 3",
        "priority": 1
    },
    {
        "Name": "Item1",
        "priority": 0
    }
]

Additional resources