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Introduction On OData(Version 8) In .Net5 Web API Application

In this article, we are going to understand the steps to integrate OData(Version 8.0) into our .Net5 application.

OData:

The OData(Open Data Protocol) is an application-level protocol for interacting with data via a RESTful interface. OData supports the description of data models, editing, and querying of data according to those models.

OData's main advantage is users can query the API results. So OData query or filter can be done in two different approaches:

Approach - 1: A response collection from an action method can be filtered by the OData. Means if action method fetched the collection of records from the database and returning to user, in the middle OData will filter the response data based on user query.

Approach - 2: Action method that returns an entity framework query of type 'IQueryable', then OData generates a SQL query based on the user OData query request, then executes against the database and then returns the result to the users.

OData query features are:
  • $select
  • $orderBy
  • $filter
  • $skip
  • $count
  • $expand

Create A .Net5 Sample Application:

Let's begin our coding by creating a sample .Net5 Web Application.

Install EF Core NuGet:

Now install ef core and SQL ef core extension Nuget package into our application.
Package Manager(Visual Studio):

Install-Package Microsoft.EntityFrameworkCore -Version 5.0.7

Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 5.0.7

.NET CLI (Visual Studio Code):

dotnet add package Microsoft.EntityFrameworkCore --version 5.0.7

dotnet add package Microsoft.EntityFrameworkCore.SqlServer --version 5.0.7

Sample SQL Script:

To follow the demo, run the SQL script to generate the table.
CREATE TABLE [dbo].[Gadgets](
	[Id] [int] IDENTITY(1,1) NOT NULL,
	[ProductName] [varchar](max) NULL,
	[Brand] [varchar](max) NULL,
	[Cost] [decimal](18, 0) NOT NULL,
	[ImageName] [varchar](1024) NULL,
	[Type] [varchar](128) NULL,
	[CreatedDate] [datetime] NULL,
	[ModifiedDate] [datetime] NULL,
PRIMARY KEY CLUSTERED 
(
	[Id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]

Setup Ef Core DbContext:

First, let's create POCO class that represents our table. So let's create a new folder 'Data', inside of it create one more folder like 'Entities'. Inside the 'Entities' folder creates our POCO class.
Data/Entities/Gadgets.cs:
namespace Dot5.Api.Odata8.Data.Entities
{
    public class Gadgets
    {
        public int Id { get; set; }
        public string ProductName { get; set; }
        public string Brand { get; set; }
        public decimal Cost { get; set; }
        public string Type { get; set; }
    }
}
In EF Core DbContext is like a database that manages all POCO classes(classes represent tables). Inside the 'Data' folder create a context class.
Data/MyWorldDbContext.cs:
using System;
using Dot5.Api.Odata8.Data.Entities;
using Microsoft.EntityFrameworkCore;

namespace Dot5.Api.Odata8.Data
{
    public class MyWorldDbContext : DbContext
    {
        public MyWorldDbContext(DbContextOptions<MyWorldDbContext> options) : base(options)
        {

        }
        public DbSet<Gadgets> Gadgets { get; set; }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
			// below line to watch the ef core sql quiries generation
			// not at all recomonded for the production code
            optionsBuilder.LogTo(Console.WriteLine);
        }
    }
}
Add database connection string into 'appsettings.Development.json'.
appsettings.Development.json:
"ConnectionStrings":{
    "MyWorldDbConnection":""
}
Register 'MyWorldDbContext' into the dependency services.
Startup.cs:
services.AddDbContext<MyWorldDbContext>(options =>
{
	options.UseSqlServer(Configuration.GetConnectionString("MyWorldDbConnection"));
});

Install OData NuGet:

Package Manage (Visual Studio):

Install-Package Microsoft.AspNetCore.OData -Version 8.0.0

.NET CLI (Visual Studio Code):

dotnet add package Microsoft.AspNetCore.OData --version 8.0.0

Configure OData Service:

Now we have to extend the 'AddControllers()' service to register our OData service. Also, we have to register our OData query types like 'Select', 'Filter', 'Count', etc.
Startup.cs:
using Microsoft.AspNetCore.OData;
using Microsoft.OpenApi.Models;

services.AddControllers()
.AddOData(option => option.Select().Filter().Count().OrderBy().Expand());

Create API Action Method Returns Queryable Results:

Let's add a new controller like 'GadgetsController' in the 'Controllers' folder. Add a new action method that returns queryable results.
Controllers/GadgetsController.cs:
using Dot5.Api.Odata8.Data;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.OData.Query;
using Microsoft.AspNetCore.OData.Routing.Controllers;
using Microsoft.AspNetCore.OData.Routing.Attributes;
using System.Linq;

namespace Dot5.Api.Odata8.Controllers
{
    [Route("gadget")]
    [ApiController]
    public class GadgetsController : ControllerBase
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public GadgetsController(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }

        
        [HttpGet("Get")]
        public IActionResult Get()
        {
            return Ok(_myWorldDbContext.Gadgets.AsQueryable());
        }    
    }
}
  • (Line: 24) Returning Querable results.

Add EnableQuery OData Attribute:

EnableQuery OData attribute needs to be decorated on top of the action method or controller so that we can use OData queries.
Controllers/GadgetsController.cs:
[EnableQuery]
[HttpGet("Get")]
public IActionResult Get()
{
	return Ok(_myWorldDbContext.Gadgets.AsQueryable());
}   

$select:

The $select system query option allows clients to request a specific set of properties for each entity or complex type. The set of properties will be comma-separated while requesting.
https://localhost:5001/gadget/Get?$select=ProductName,Cost

Our action method return type is 'Queryable', and our '$select' operator requested only 2props in the above URL, So our entity framework query generates as below.

$filter:

The $filter filters data based on a boolean condition. The following are conditional operators that have to be used in URLs.
  • eq - equals to.
  • ne - not equals to
  • gt - greater than
  • ge - greater than or equal 
  • lt - less than
  • le - less than or equal
https://localhost:5001/gadget/Get?$filter=ProductName eq 'Think Pad'

Now let's see how entity framework core SQL query generated.

$orderby:

The $orderby sorts the data using 'asc' and 'desc' keywords. We can do sorting on multiple properties using comma separation.
https://localhost:5001/gadget/Get?$orderby=Id desc


Now let's see the SQL query generated by the entity framework core.

$top:

The $top fetches specified the count of top records in the collection. So to work this operator, we must specify an extension method like 'SetMaxTo(specify_max_number)'.
Startup.cs:
services.AddControllers()
.AddOData(option => option.Select().Filter().Count().OrderBy().Expand()
.SetMaxTop(100));

https://localhost:5001/gadget/Get?$top=2

Now let's see the SQL query generated by the entity framework core.

$skip:

The $skip skips the specified number of records and fetches the remaining data.
https://localhost:5001/gadget/Get?$skip=5


Now let's see the SQL query generated by the entity framework core.

$expand:

Using $expand can query the internal or navigation property object.

First, let's create models of complex object types. So lets' create a new folder like 'Models'. Inside the 'Models' folder let's create a class like 'Person' and 'BankAccounts' with mapping navigation property.
Models/Person.cs:
using System.Collections.Generic;

namespace Dot5.Api.Odata8.Controllers.Models
{
    public class Person
    {
        public int Id { get; set; }
        public string Name { get; set; }
        public List<BankAccount> BankAccounts { get; set; }
    }

    public class BankAccount
    {
        public int AccountId { get; set; }
        public string BankName { get; set; }
    }
}
Now let's create a new action method that returns some fake 'Person' type response.
Controllers/GadgetsController.cs:
[HttpGet("person")]
[EnableQuery]
public IActionResult GetPerson()
{
	var person = new Person
	{
		Name = "Naveen",
		Id = 1,
		BankAccounts = new List<BankAccount>
		{
			new BankAccount
			{
				AccountId = 1111,
				BankName = "Bank 1"
			},
			new BankAccount
			{
				AccountId = 2222,
				BankName = "Bank 2"
			}
		}
	};
	var result = new List<Person>();
	result.Add(person);
	return Ok(result);
}
  • Here I'm returning direct collection means not Queriable response. So from this, we can understand that the OData query filter can be applied on entity framework core and normal collection results.
https://localhost:5001/gadget/person?$expand=BankAccounts($select=AcccountId)

$count:

In an original OData, the response contains some additional OData properties like '@odata.context', '@odata.nextLink', '@odata.count', etc. If we observe our above responses all these OData properties do not exist, that is because the above implementation uses normal Web API routing. So $count can't be seen with the above implementation. So to make $count work we will implement Odata routing.

So let's create a new controller like 'GadgetsOdataController' in the controller's folder.
Controllers/GadgetsOdataController.cs:
using Dot5.Api.Odata8.Data;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.OData.Query;

namespace Dot5.Api.Odata8.Controllers
{
    public class GadgetsOdataController:ControllerBase
    {
        private readonly MyWorldDbContext _myWorldDbContext;
        public GadgetsOdataController(MyWorldDbContext myWorldDbContext)
        {
            _myWorldDbContext = myWorldDbContext;
        }

        [EnableQuery]
        public IActionResult Get()
        {
            return Ok(_myWorldDbContext.Gadgets.AsQueryable());
        }
    }
}
  • Here the difference between 'GadgetsController.cs' and 'GadgetsOdataController.cs' is routing, which means the Web API attribute routing must be removed here.
Now in the above action method, our return object type is 'Gadgets' so now we have to register our 'Gadgets' type with OData EDM. The Entity Data Model is used to map our response type so that the OData engine can analyze its queries. So in the 'Startup.cs' class let's create a method that returns the 'EDM'.
Startup.cs:
public static IEdmModel GetEdmModel()
{
	ODataConventionModelBuilder modelBuilder = new ODataConventionModelBuilder();
	modelBuilder.EntitySet<Gadgets>("GadgetsOdata");
	return modelBuilder.GetEdmModel();
}
  • (Line: 4) Our 'Gadgets' registered as 'EnitySet' with a name like 'GadgetsOdata'. Here the name of the entity should match with our controller(eg: GadgetsOdataController) because this name will be used as part of our URL path by OData.
Now we need to register 'GetEdmModel' method with 'AddRouteComponents()' extension method in OData.
Startup.cs:
services.AddControllers()
.AddOData(option => option.Select().Filter()
.Count().OrderBy().Expand().SetMaxTop(100)
.AddRouteComponents("odata",GetEdmModel()));
Here "Odata" will be used as a route prefix for all the models registered in the 'GetEdmModel'.

Now our OData route looks as below:
https://localhost:5001/odata/GadgetsOdata


So from above, we can confirm that our response will have OData properties. So we can query $count now.
https://localhost:5001/odata/GadgetsOdata?$count=true


So that's all about a small introduction on OData(V8) in .Net5 Web API application.

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Wrapping Up:

Hopefully, I think this article delivered some useful information on OData Version 8. I love to have your feedback, suggestions, and better techniques in the comment section below.

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Comments

  1. Hi, can I download this project?

    ReplyDelete
  2. Great article, interesting about security.

    ReplyDelete
  3. This is exactly the article I was looking for. Thanks. What this article contained that the other articles I had been reading missed was explaining both the "out of the box" OData functionality and the EDMModel functionality in one article. Also the look and feel of the page makes the explanation easier to follow

    ReplyDelete
  4. Hello There, suppose on the api return I want to return one custom class which utilizes some multiple odata entities and fetch the data from different table and return. For that new class or new entity (Which is not a db table) how can i enable the OData. count property.

    ReplyDelete
  5. "Here the name of the entity should match with our controller(eg: GadgetsOdataController) because this name will be used as part of our URL path by OData." Thank you very much, that was the missing hint I needed. I followed several tutorials and never could get the $count to work because I just took my User collection but the controller was named AccountController

    ReplyDelete

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