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A Small Demo On OData(v8) In .NET 7 API Application

In this article, we are going to implement a sample on OData in .NET7 API application.

OData:

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

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

Sample SQL Table Scripts:

Let's run the below sample SQL script to create a table like 'Employee'.
Sample SQL Script:
Create Table Employee(
Id INT IDENTITY(1,1) NOT NULL,
FirstName VARCHAR(200) NULL,
LastName VARCHAR(200) NULL,
Salary Decimal(18,2) NULL,
JobRole VARCHAR(50) NULL
CONSTRAINT PK_Employee PRIMARY KEY (Id)
)

Create .NET7 Web API Application:

Let's create the .NET 7 Web API application to accomplish our demo. Here to create .NET 7 application we use IDE's(editors) either Visual Studio 2022 or Visual Studio Code(Using .NET CLI command). In this demo, we are going to use Visual Studio Code(using .NET CLI command)

.NET CLI command to create API project.
dotnet new webapi -o name_of_your_project

Install Entity Framework Core NuGet Package:

Let's install the entity framework core NuGet package.

Visual Studio 2022:
Install-Package Microsoft.EntityFrameworkCore -Version 7.0.3

Visual Studio Code:
dotnet add package Microsoft.EntityFrameworkCore --version 7.0.3

Let's install the entity framework core SQL NuGet package.

Visual Studio 2022:
Install-Package Microsoft.EntityFrameworkCore.SqlServer -Version 7.0.3

Visual Studio Code:
dotnet add package Microsoft.EntityFrameworkCore.SqlServer --version 7.0.3

Create DatabaseContext:

Let's create an 'Employee' class in 'Data/Entities' folder(new folders) that represents our 'Employee' table.
Data/Entities/Employee.cs:
namespace Dot7.OData.Demo.Data.Entities;
public class Employee
{
    public int Id{get;set;}
    public string? FirstName{get;set;}
    public string? LastName{get;set;}
    public decimal? Salary{get;set;}
    public string? JobRole{get;set;}
}
Let's create our database context class like 'MyWorldDbContext.cs' in 'Data' folder.
Data/MyWorldDbContext.cs:
using Dot7.OData.Demo.Data.Entities;
using Microsoft.EntityFrameworkCore;
namespace Dot7.OData.Demo.Data;
public class MyWorldDbContext : DbContext
{
    public MyWorldDbContext(DbContextOptions<MyWorldDbContext> options) : base(options)
    {
    }
    public DbSet<Employee> Employee { get; set; }
}
  • (Line: 4) The 'Microsoft.EntityFrameworkCore.DbContext' needs to be inherited by our 'MyWorldDbContext' to act as a Database context class.
  • (Line: 6) The 'Microsoft.EntityFrameworkDbContextOptions' is an instance of options that we are going to register in 'Program.cs' like 'database provider', 'connection string', etc.
  • (Line: 9) Our table classes must be registered inside of our database context class with 'DbSet<T>' so the entity framework can communicate with the tables of the database.
Now let's add the connection string into the 'appsettings.Development.json'.
appsettings.Development.json:
"ConnectionStrings": {
  "MyWorldDbConnection": "Data Source=(localdb)\\MSSQLLocalDB;Initial Catalog=MyWorldDB;Integrated Security=True;Connect Timeout=30"
}
Now let's register our DatabaseContext into our 'Program.cs'.
Program.cs:
builder.Services.AddDbContext<MyWorldDbContext>(options => {
    options.UseSqlServer(builder.Configuration.GetConnectionString("MyWorldDbConnection"));
});

Create An 'EmployeeController': 

Let's create a new controller like 'EmployeeController'.
Controllers/EmployeeController.cs:
using Dot7.OData.Demo.Data;
using Microsoft.AspNetCore.Mvc;
namespace Dot7.OData.Demo.Controllers;
[ApiController]
[Route("[controller]")]
public class EmployeeController: ControllerBase
{
    private readonly MyWorldDbContext _myWorldDbContext;
    public EmployeeController(MyWorldDbContext myWorldDbContext)
    {
        _myWorldDbContext = myWorldDbContext;
    }
}
  • Here injected our 'MyWordDbContext'(database context) into the controller constructor.

Install OData NuGet Package:

Let's install the OData NuGet Package.

Visual Studio 2022:
Install-Package Microsoft.AspNetCore.OData -Version 8.0.12

Visual Studio Code:
dotnet add package Microsoft.AspNetCore.OData --version 8.0.12

Register 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.
Program.cs:
builder.Services.AddControllers().AddOData(options =>
    options.Select().Filter().Count().OrderBy().Expand());

Create Action Method With Queriable Return Type:

Let's create an action method of the queriable return type.
Controllers/EmployeeController.cs:
[HttpGet]
public IActionResult Get()
{
	return Ok(_myWorldDbContext.Employee.AsQueryable());
}
  • Here we use 'AsQueryable()' method.

OData EnableQuery Attribute:

EnableQuery OData attribute needs to be decorated on top of the action method or controller so that we can use OData queries.
Controller/EmployeeController.cs:
using Microsoft.AspNetCore.OData.Query;

[EnableQuery]
[HttpGet]
public IActionResult Get()
{
	return Ok(_myWorldDbContext.Employee.AsQueryable());
}

$select:

The $select system query option allows clients to request a specific set of properties for each entity or complex type. The set of properties will be comma separated while requesting.
http://localhost:5093/employee?$select=firstname,salary


The '$select' operator requested only 2-props 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

http://localhost:5093/employee?$filter=salary eq 19000

Now let's see how the entity framework core generates filter query

$orderby:

The $orderby sorts the data using 'asc' and 'desc' keywords. We can do sorting on multiple properties using comma separation.
http://localhost:5093/employee?$orderby=id desc

Let's observe the query generated by the entity framework core.

$skip:

The $skip skips the specified number of records and fetches the remaining data
http://localhost:5093/employee?$skip=2


Let's check the query generated by the entity framework core.

$top:

The $top fetches specified the count of top records in the collection. so to work this operator, we must specify an extension method like 'SetMaxTo(specify_max_number)'.
Program.cs:
builder.Services.AddControllers().AddOData(options =>
    options.Select().Filter().Count().OrderBy().Expand().SetMaxTop(100));
  • Here 'SetMaxTop' method configure with '100' means maximum top 100 records.
http://localhost:5093/employee?$top=2

Let's check the query generated by the entity framework core.

SQL Child Table Script(With Onet-To-Many Relationship):

Let's create a child table like 'EmployeeAddresses' for the 'Employee' table with a one-to-many relationship.
Sample EmployeeAddresses Script:
Create Table EmployeeAddresses(
Id int IDENTITY (1,1) NOT NULL,
HouseNumber VARCHAR(100),
City VARCHAR(100),
State VARCHAR(100),
Country varchar(100),
EmployeeId int NOT NULL
CONSTRAINT PK_Employee_Addresses_Id PRIMARY KEY (Id)
CONSTRAINT FK_Employee_Addresses_EmployeeId FOREIGN KEY (EmployeeId)
REFERENCES Employee (Id)
)

Create EmployeeAddresses Entity And Configure With DatabaseContext:

Let's create a 'EmployeeAddresses' entity in the 'Data/Entities' folder.
Data/Entities/EmployeeAddresses:
namespace Dot7.OData.Demo.Data.Entities;
public class EmployeeAddresses
{
    public int Id { get; set; }
    public string? HouseNumber { get; set; }
    public string? City { get; set; }
    public string? State { get; set; }
    public string? Country { get; set; }
    public int EmployeeId { get; set; }
    public Employee Employee { get; set; }
}
  • (Line: 10) The 'Employee' is a navigation property that says one 'EmployeeAdresses' can have one 'Employee'.
Now in the 'Employee' class, we need to add the navigation property of 'EmployeeAddresses' that says one 'Employee' can have multiple 'EmployeeAddress'.
Data/Entities/Employee.cs:
namespace Dot7.OData.Demo.Data.Entities;
public class Employee
{
    public int Id { get; set; }
    public string? FirstName { get; set; }
    public string? LastName { get; set; }
    public decimal? Salary { get; set; }
    public string? JobRole { get; set; }
    public List<EmployeeAddresses> EmployeeAddresses { get; set; }
}
Now update our DatabaseContext as follow:
Entities/MyWorldDbContext.cs:
using Dot7.OData.Demo.Data.Entities;
using Microsoft.EntityFrameworkCore;
namespace Dot7.OData.Demo.Data;
public class MyWorldDbContext : DbContext
{
    public MyWorldDbContext(DbContextOptions<MyWorldDbContext> options) : base(options)
    {

    }
    public DbSet<Employee> Employee { get; set; }
    public DbSet<EmployeeAddresses> EmployeeAddresses { get; set; }
    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.Entity<EmployeeAddresses>()
        .HasOne(_ => _.Employee)
        .WithMany(_ => _.EmployeeAddresses)
        .HasForeignKey(_ => _.EmployeeId);
    }
}
  • (Line: 14-17) Here using fluent API we configured one to many relationships between 'Employee' and 'EmployeeAddresses'.

$expand:

Using $expand we can query the internal or navigating property object. So we have to assign the navigation property name to the '$expand' then we can apply all other operations like '$select', '$filter', '$skip' on the navigation property type.
http://localhost:5093/Employee?$expand=EmployeeAddresses($select=Id, city)


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

$count:

In an original OData, the response contains some additional OData properties like '@odata.context', '@odata.nextLink', '@Odata.count', etc. If we observe in all previous responses in this article doesn't contain the data properties, that is because the implementation uses normal web API routing. So $count can't be seen with the above implementation. So to make $count work we need to implement odata routing.

So let's create a new controller like 'EmployeeODataController' in the controller's folder.
Controllers/EmployeeODataController.cs:
using Dot7.OData.Demo.Data;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.OData.Query;
namespace Dot7.OData.Demo.Controllers;
public class EmployeeODataController:ControllerBase
{
    private readonly MyWorldDbContext _myWorldDbContext;
    public EmployeeODataController(MyWorldDbContext myWorldDbContext)
    {
        _myWorldDbContext = myWorldDbContext;
    }
    [EnableQuery]
    public IActionResult Get()
    {
        return Ok(_myWorldDbContext.Employee.AsQueryable());
    }
}
  • Here the difference between 'EmployeeController.cs' and 'EmployeeODataController.cs' is removed the 'ApiController' and 'RouteController' which means we disabled the Asp.Net Core Web API routing.
Now in the above action method, our return type is 'Employee', so we have to register the our 'Employee' type with OData EDM(Entity Data Model). The Entity Data Model is used to map our response type so that the OData engine can analyze its queries. So in 'Program.cs' let's crate method that will return the ODATA EDM.
Program.cs:
static IEdmModel GetEdmModel()
{
	ODataConventionModelBuilder modelBuilder = new ODataConventionModelBuilder();
	modelBuilder.EntitySet<Employee>("EmployeeOData");
	return modelBuilder.GetEdmModel();
}
  • (Line: 4) Our 'Employee'(response model or entity class) registered as 'EntitySet' with name like 'EmployeeOData'. Here the name("EmployeeOData") should match our controller name("EmployeeODataController") because this name going to be used as part of the URL.
Now we need to register our 'GetEdmModel' method with 'AddRouteComponents()'.
Program.cs:
builder.Services.AddControllers()
.AddOData(options =>
    options.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'.
So our new odata endpoint looks like below
http://localhost:5093/odata/EmployeeOData

  • Here we can see our odata property like '@odata.context'
So our URL with '$count' looks as below
http://localhost:5093/odata/EmployeeOData?$count=true

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Wrapping Up:

Hopefully, I think this article delivered some useful information on OData Version 8 in .NET7 API. I love to have your feedback, suggestions, and better techniques in the comment section below.

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