OData Query Options in ASP.NET Core OData 8

Applies To:# OData Web API 8 supported OData Web API v8

ASP.NET Core OData 8.x provides out of the box querying capabilities.

A query option is basically requesting that a service perform a set of transformations such as filtering, sorting, etc. to its data before returning the results.

There are various types of query options:

• System query options - Query options that are defined by OData. System query options are prefixed with the dollar ($) character, which is optional in OData 4.01. Example is $filter.
• Parameter aliases - Parameter aliases can be used in place of literal values in entity keys, function parameters, or within a $compute, $filter or $orderby expression. Example http://host/service.svc/Employees?$filter=Region eq @p1&@p1='WA'.
• Custom query options - Custom query options are not defined in the OData specification. They are defined by the users. They MUST NOT begin with the $ or @ character and MUST NOT conflict with any OData-defined system query options. Example http://host/service/Products?debug-mode=true.

See more information on the types of query options here.

This tutorial demonstrates how to use query options in ASP.NET Core OData 8.x.

Model classes

We will define our model as follows:

public class Customer
{
    [Key]
    public int Id { get; set; }
    public String Name { get; set; }
    public int Age { get; set; }
    public List<Order> Orders { get; set; }
}

public class Order
{
    [Key]
    public int Id { get; set; }
    public int Price { get; set; }
    public int Quantity { get; set; }
}

We have a Customer entity with Orders navigation property. We define a one to many relationship between Customer and Order entities. One Customer can have one or more Orders. Read more on OData data model and Entity relations.

Registering OData services

.NET 6.0

// Program.cs
var builder = WebApplication.CreateBuilder(args);

var modelBuilder = new ODataConventionModelBuilder();
modelBuilder.EntitySet<Customer>("Customers");

builder.Services.AddControllers().AddOData(
    options => options.Select().Filter().OrderBy().Expand().Count().SetMaxTop(null).AddRouteComponents(
        routePrefix: "odata",
        model: modelBuilder.GetEdmModel()));

var app = builder.Build();

.NET Core 3.1

// Startup.cs
public void ConfigureServices(IServiceCollection services)
{
    var modelBuilder = new ODataConventionModelBuilder();
    modelBuilder.EntitySet<Customer>("Customers");

    services.AddControllers().AddOData(
            options => options.Select().Filter().OrderBy().Expand().Count().SetMaxTop(null).AddRouteComponents(
                "odata",
                modelBuilder.GetEdmModel()));
}

In the above configuration, options is an instance of ODataOptions.

• Select() enables $select query option.
• Filter() enables $filter query option.
• OrderBy() enables $orderby query option.
• Expand() enables $expand query option.
• Count() enables $count query option.
• SetMaxTop() sets the maximum value of $top that a client can request. Read more in the client-driven paging documentation

If you want to enable all query options at once, you would call options.EnableQueryFeatures().

Controller

public class CustomersController : ODataController
{
    private static List<Order> Orders = new List<Order>
    {
        new Order { Id = "1001", Price = 10, Quantity = 10 },
        new Order { Id = "1002", Price = 35, Quantity = 2 },
        new Order { Id = "1003", Price = 70, Quantity = 5 },
        new Order { Id = "1004", Price = 20, Quantity = 20 },
        new Order { Id = "1005", Price = 40, Quantity = 15 },
        new Order { Id = "1006", Price = 15, Quantity = 50 },
    };

    private static List<Customer> Customers = new List<Customer>
    {
        new Customer { Id = 1, Name = "Customer 1", Age = 31, Orders = new List<Order>(){Orders[0], Orders[1]} },
        new Customer { Id = 2, Name = "Customer 2", Age = 32, Orders = new List<Order>(){Orders[2], Orders[3]} },
        new Customer { Id = 3, Name = "Customer 3", Age = 33, Orders = new List<Order>(){Orders[4], Orders[5]} }
    };

    [EnableQuery]
    public IActionResult Get()
    {
        return Ok(Customers);
    }
}

In the preceding code, the Get controller method is decorated with the EnableQuery attribute. The EnableQuery attribute is an action filter that parses, validates, and applies the query. The filter converts the query options into a LINQ (Language-Integrated Query) expression. When the controller returns an IQueryable or IActionResult type, the LINQ provider converts the LINQ expression into a query, e.g., Entity Framework (EF) Core will convert the LINQ expression into an SQL statement.

Basic queries

We can select a specific property or properties in an entity:

GET http://localhost:6285/odata/Customers?$select=Name

{
    "@odata.context": "http://localhost:6285/odata/$metadata#Customers(Name)",
    "value": [
        {
            "Name": "Customer 1"
        },
        {
            "Name": "Customer 2"
        },
        {
            "Name": "Customer 3"
        }
    ]
}

We can return Customers with their related Orders. In this case we use $expand:

GET http://localhost:6285/odata/Customers?$expand=Orders

{
    "@odata.context": "http://localhost:6285/odata/$metadata#Customers(Orders())",
    "value": [
        {
            "Id": 1,
            "Name": "Customer 1",
            "Age": 31,
            "Orders": [
                {
                    "Id": 1002,
                    "Price": 35,
                    "Quantity": 2
                },
                {
                    "Id": 1001,
                    "Price": 10,
                    "Quantity": 10
                }
            ]
        },
        {
            "Id": 2,
            "Name": "Customer 2",
            "Age": 32,
            "Orders": [
                {
                    "Id": 1004,
                    "Price": 20,
                    "Quantity": 20
                },
                {
                    "Id": 1003,
                    "Price": 70,
                    "Quantity": 5
                }
            ]
        },
        {
            "Id": 3,
            "Name": "Customer 3",
            "Age": 33,
            "Orders": [
                {
                    "Id": 1006,
                    "Price": 15,
                    "Quantity": 50
                },
                {
                    "Id": 1005,
                    "Price": 40,
                    "Quantity": 15
                }
            ]
        }
    ]
}

We can combine various query options. In the request below:

• Select only the Name property from Customer entity.
• Expand the related Orders.
• Filter the Orders and return only the ones whose Id is greater than 1004.
• Order the Customers by Name in descending order.

http://localhost:6285/odata/Customers?$select=Name&$expand=Orders($filter=Id gt 1004)&$orderby=Name desc

{
    "@odata.context": "http://localhost:6285/odata/$metadata#Customers(Name,Orders())",
    "value": [
        {
            "Name": "Customer 3",
            "Orders": [
                {
                    "Id": 1006,
                    "Price": 15,
                    "Quantity": 50
                },
                {
                    "Id": 1005,
                    "Price": 40,
                    "Quantity": 15
                }
            ]
        },
        {
            "Name": "Customer 2",
            "Orders": []
        },
        {
            "Name": "Customer 1",
            "Orders": []
        }
    ]
}

Limiting query options

We can limit the type of query option that can be used while calling a certain API.

public class CustomersController : ODataController
{
    [EnableQuery(AllowedQueryOptions = AllowedQueryOptions.Filter)]
    public IActionResult Get()
    {
        return Ok(Customers);
    }
}

In the controller method above, we only allow $filter query option. If we use another query option e.g $select, we will get an error.

GET http://localhost:6285/odata/Customers?$select=Name

{
    "error": {
        "code": "",
        "message": "The query specified in the URI is not valid. Query option 'Select' is not allowed. To allow it, set the 'AllowedQueryOptions' property on EnableQueryAttribute or QueryValidationSettings.",
        "details": [],
        "innererror": {}
    }
}

We can combine multiple query options as shown below:

[EnableQuery(AllowedQueryOptions = AllowedQueryOptions.Filter | AllowedQueryOptions.OrderBy)]
public IQueryable<Customer> Get()
{
    return Customers.AsQueryable<Customer>();
}

Configured vs allowed query options

When registering OData services, we add query options configurations as shown below:

.AddOData(
    options => options.Select().OrderBy().Expand().Count().SetMaxTop(null)
)

These are global configurations. If a query option is not enabled here, it cannot be enabled in the controller.

In the above example, we did not enable the $filter query option. If we configure a controller as shown below, the $filter will not be applied since it's not enabled in the global configuration.

[EnableQuery(AllowedQueryOptions = AllowedQueryOptions.Filter)]
public IActionResult Get()
{
    return Ok(Customers);
}

Applying query options directly

There are scenarios where we may be unable to use EnableQuery attribute. For example, if our controller fetches data from multiple data sources and not just a single IQueryable, we may want to control how the query options are applied and process the data before it's returned by the controller.

We use the ODataQueryOptions.ApplyTo method to apply the required query options.

ODataQueryOptions<TEntity> can be used an argument in a controller method:

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    IQueryable results = options.ApplyTo(Customers.AsQueryable());

    return results as IQueryable<Customer>;
}

In the example above, the ApplyTo method applies to all query options.

We can call ApplyTo on individual query options as shown in the subsections below.

SelectExpand query

We can call ApplyTo on the SelectExpand property of ODataQueryOptions class as follows:

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    IQueryable results = options.SelectExpand.ApplyTo(Customers.AsQueryable(), new ODataQuerySettings());

    return results as IQueryable<Customer>;
}

SelectExpand handles both $select and $expand query options.

The options.SelectExpand property is an instance of SelectExpandQueryOption. It will be set when we make the request below:

GET http://localhost:6285/odata/Customers?$expand=Orders

If we don't want to pass the query option in the request, but we want the Orders property to be expanded, we can initialize the SelectExpandQueryOption and set it in the request URL.

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    options.Request.ODataFeature().SelectExpandClause = new SelectExpandQueryOption(null, "Orders", options.Context,
        new ODataQueryOptionParser(
            model: options.Context.Model,
            targetEdmType: options.Context.NavigationSource.EntityType(),
            targetNavigationSource: options.Context.NavigationSource,
            queryOptions: new Dictionary<string, string> { { "$expand", "Orders" } },
            container: options.Context.RequestContainer)).SelectExpandClause;

    IQueryable results = options.ApplyTo(Customers.AsQueryable());

    return results as IQueryable<Customer>;
}

When making the request, we don't need to include the $expand query option.

GET http://localhost:6285/odata/Customers

Below will be the output:

{
    "@odata.context": "http://localhost:6285/odata/$metadata#Customers(Orders())",
    "value": [
        {
            "Id": 1,
            "Name": "Customer 1",
            "Age": 31,
            "Orders": [
                {
                    "Id": 1001,
                    "Price": 10,
                    "Quantity": 10
                },
                {
                    "Id": 1002,
                    "Price": 35,
                    "Quantity": 2
                }
            ]
        },
        ...
        ...
    ]
}

Filter query

We can call ApplyTo on the Filter property of ODataQueryOptions class as follows:

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    IQueryable results = options.Filter.ApplyTo(Customers.AsQueryable(), new ODataQuerySettings());

    return results as IQueryable<Customer>;
}

The options.Filter property is an instance of FilterQueryOption. It will be set when we make the request below:

GET http://localhost:6285/odata/Customers?$filter=Id eq 1

If we don't want to pass the filter query option in the request URL, but we want a filter to be applied, we can initialize the FilterQueryOption and call ApplyTo to apply the filter query to the data.

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    var filter = new FilterQueryOption("Id eq 1", options.Context,
        new ODataQueryOptionParser(
            model: options.Context.Model,
            targetEdmType: options.Context.NavigationSource.EntityType(),
            targetNavigationSource: options.Context.NavigationSource,
            queryOptions: new Dictionary<string, string> { { "$filter", "Id eq 1" } },
            container: options.Context.RequestContainer));

    IQueryable results = filter.ApplyTo(Customers.AsQueryable(), new ODataQuerySettings());

    return results as IQueryable<Customer>;
}

When making the request, we don't need to include the $filter query option.

GET http://localhost:6285/odata/Customers

Below will be the output:

{
    "@odata.context": "http://localhost:6285/odata/$metadata#Customers",
    "value": [
        {
            "Id": 1,
            "Name": "Customer 1",
            "Age": 31
        }
    ]
}

Apply query

The $apply query option is used in grouping and aggregating data.

We can call ApplyTo on the Apply property of ODataQueryOptions class as follows:

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    IQueryable results = options.Apply.ApplyTo(Customers.AsQueryable(), new ODataQuerySettings());

    return results as IQueryable<Customer>;
}

The options.Apply property is an instance of ApplyQueryOption. It will be set when we make the request below:

GET http://localhost:6285/odata/Customers?$apply=aggregate(Age with max as MaxAge)

If we don't want to pass the query option in the request, but we want to aggregate the results, we can initialize the ApplyQueryOption and set it in the request.

public IQueryable<Customer> Get(ODataQueryOptions<Customer> options)
{
    var queryOptionParser = new ODataQueryOptionParser(
            model: options.Context.Model,
            targetEdmType: options.Context.NavigationSource.EntityType(),
            targetNavigationSource: options.Context.NavigationSource,
            queryOptions: new Dictionary<string, string> { { "$apply", "aggregate(Age with max as MaxAge)" } },
            container: options.Context.RequestContainer);

    options.Request.ODataFeature().ApplyClause = new ApplyQueryOption("aggregate(Age with max as MaxAge)", options.Context, queryOptionParser).ApplyClause;

    IQueryable results = options.ApplyTo(Customers.AsQueryable());

    return results as IQueryable<Customer>;
}

Extending the EnableQueryAttribute class

The EnableQueryAttribute class can be extended.

EnableQueryAttribute class has several public virtual methods that can be overridden.

• ValidateQuery - performs query validation before query execution. In this method, we call each query option's Validate method and use the appropriate validator class to perform validation.
• ApplyQuery - triggers queryOption.ApplyTo().
• GetModel - returns an IEdmModel.

public class CustomEnableQueryAttribute : EnableQueryAttribute
{
    public override void ValidateQuery(HttpRequestMessage request, ODataQueryOptions queryOptions)
    {
        if (queryOptions.Filter != null)
        {
            queryOptions.Filter.Validator = new MyFilterValidator();
        }
        base.ValidateQuery(request, queryOptions);
    }
}

public class MyFilterValidator : FilterQueryValidator
{
    public override void Validate(FilterQueryOption filterOption, ODataValidationSettings validationSettings)
    {
        ValidateRangeVariable(filterOption.FilterClause.RangeVariable, validationSettings);

        base.Validate(filterOption, validationSettings);
    }

    public override void ValidateRangeVariable(RangeVariable rangeVariable, ODataValidationSettings settings)
    {
        // Add your custom logic to Validate RangeVariable
    }
}

The CustomEnableQuery attribute can be applied to a controller action as follows:

[CustomEnableQuery]
public IQueryable<Customer> Get()
{
    return Customers.AsQueryable<Customer>();
}

The MyFilterValidator will only be used in $filter queries. In other queries, the default validators will be used.