Filtering

With Hot Chocolate filters, you can expose complex filter objects through your GraphQL API that translates to native database queries. The default filter implementation translates filters to expression trees that are applied to IQueryable. Hot Chocolate by default will inspect your .NET model and infer the possible filter operations from it. Filters use IQueryable (IEnumerable) by default, but you can also easily customize them to use other interfaces.

The following type would yield the following filter operations:

public class Foo
{
    public string Bar { get; set; }
}

SDL

input FooFilterInput {
  and: [FooFilterInput!]
  or: [FooFilterInput!]
  name: StringOperationFilterInput
}

input StringOperationFilterInput {
  and: [StringOperationFilterInput!]
  or: [StringOperationFilterInput!]
  eq: String
  neq: String
  contains: String
  ncontains: String
  in: [String]
  nin: [String]
  startsWith: String
  nstartsWith: String
  endsWith: String
  nendsWith: String
}

Getting started

Filtering is part of the HotChocolate.Data package. You can add the dependency with the dotnet cli

Bash

dotnet add package HotChocolate.Data

To use filtering you need to register it on the schema:

services.AddGraphQLServer()
  // Your schema configuration
  .AddFiltering();

Hot Chocolate will infer the filters directly from your .Net Model and then use a Middleware to apply filters to IQueryable<T> or IEnumerable<T> on execution.

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

⚠️ Note: If you use more than one middleware, keep in mind that ORDER MATTERS. The correct order is UsePaging > UseProjections > UseFiltering > UseSorting

Customization

Under the hood, filtering is based on top of normal Hot Chocolate input types. You can easily customize them with a very familiar fluent interface. The filter input types follow the same descriptor scheme as you are used to from the normal input types. Just extend the base class FilterInputType<T> and override the descriptor method.

IFilterInputTypeDescriptor<T> supports most of the methods of IInputTypeDescriptor<T>. By default filters for all fields of the type are generated. If you do want to specify the filters by yourself you can change this behavior with BindFields, BindFieldsExplicitly or BindFieldsImplicitly. When fields are bound implicitly, meaning filters are added for all properties, you may want to hide a few fields. You can do this with Ignore(x => Bar). It is also possible to customize the GraphQL field of the operation further. You can change the name, add a description or directive.

public class UserFilterType : FilterInputType<User>
{
    protected override void Configure(
        IFilterInputTypeDescriptor<User> descriptor)
    {
        descriptor.BindFieldsExplicitly();
        descriptor.Field(f => f.Name).Name("custom_name");
    }
}

If you want to limit the operations on a field, you need to declare you own operation type. Given you want to only allow eq and neq on a string field, this could look like this

public class UserFilterType : FilterInputType<User>
{
    protected override void Configure(
        IFilterInputTypeDescriptor<User> descriptor)
    {
        descriptor.BindFieldsExplicitly();
        descriptor.Field(f => f.Name).Type<CustomStringFilterType>();
    }
}

public class CustomerOperationFilterInput : StringOperationFilterInput
{
    protected override void Configure(IFilterInputTypeDescriptor descriptor)
    {
        descriptor.Operation(DefaultFilterOperations.Equals);
        descriptor.Operation(DefaultFilterOperations.NotEquals);
    }
}

SDL

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  name: CustomerOperationFilterInput
}

input CustomerOperationFilterInput {
  and: [CustomerOperationFilterInput!]
  or: [CustomerOperationFilterInput!]
  eq: String
  neq: String
}

To apply this filter type we just have to provide it to the UseFiltering extension method with as the generic type argument.

public class Query
{
    [UseFiltering(typeof(UserFilterType))]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

"and" / "or" Filter

There are two built in fields.

and: Every condition has to be valid
or : At least one condition has to be valid

Example:

GraphQL

query {
  posts(
    first: 5
    where: {
      or: [{ title: { contains: "Doe" } }, { title: { contains: "John" } }]
    }
  ) {
    edges {
      node {
        id
        title
      }
    }
  }
}

⚠️ or does not work when you use it like this:

GraphQL

query {
  posts(
    first: 5
    where: { title: { contains: "John", or: { title: { contains: "Doe" } } } }
  ) {
    edges {
      node {
        id
        title
      }
    }
  }
}

In this case the filters are applied like title.Contains("John") && title.Contains("Doe") rather than title.Contains("John") || title.Contains("Doe") how you probably intended it.

Removing "and" / "or"

If you do not want to expose and and or you can remove these fields with the descriptor API:

public class UserFilterType : FilterInputType<User>
{
    protected override void Configure(
        IFilterInputTypeDescriptor<User> descriptor)
    {
        descriptor.AllowAnd(false).AllowOr(false);
    }
}

Filter Types

Boolean Filter

Defined the filter operations of a bool field.

public class User
{
    public bool IsOnline { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input BooleanOperationFilterInput {
  eq: Boolean
  neq: Boolean
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  isOnline: BooleanOperationFilterInput
}

Comparable Filter

Defines filters for IComparables like: bool, byte, shot, int, long, float, double decimal, Guid, DateTime, DateTimeOffset and TimeSpan

public class User
{
    public int LoginAttempts { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input ComparableOperationInt32FilterInput {
  eq: Int
  neq: Int
  in: [Int!]
  nin: [Int!]
  gt: Int
  ngt: Int
  gte: Int
  ngte: Int
  lt: Int
  nlt: Int
  lte: Int
  nlte: Int
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  loginAttempts: ComparableOperationInt32FilterInput
}

String Filter

Defines filters for string

public class User
{
    public string Name { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input StringOperationFilterInput {
  and: [StringOperationFilterInput!]
  or: [StringOperationFilterInput!]
  eq: String
  neq: String
  contains: String
  ncontains: String
  in: [String]
  nin: [String]
  startsWith: String
  nstartsWith: String
  endsWith: String
  nendsWith: String
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  name: StringOperationFilterInput
}

Enum Filter

Defines filters for C# enums

public enum Role {
  Default,
  Moderator,
  Admin
}

public class User
{
    public Role Role { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input RoleOperationFilterInput {
  eq: Role
  neq: Role
  in: [Role!]
  nin: [Role!]
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  kind: RoleOperationFilterInput
}

Object Filter

An object filter is generated for all nested objects. The object filter can also be used to filter over database relations. For each nested object, filters are generated.

public class User
{
    public Address Address { get; set; }
}

public class Address
{
    public string Street { get; set; }

    public bool IsPrimary { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input AddressFilterInput {
  and: [AddressFilterInput!]
  or: [AddressFilterInput!]
  street: StringOperationFilterInput
  isPrimary: BooleanOperationFilterInput
}

input BooleanOperationFilterInput {
  eq: Boolean
  neq: Boolean
}

input StringOperationFilterInput {
  and: [StringOperationFilterInput!]
  or: [StringOperationFilterInput!]
  eq: String
  neq: String
  contains: String
  ncontains: String
  in: [String]
  nin: [String]
  startsWith: String
  nstartsWith: String
  endsWith: String
  nendsWith: String
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  address: AddressFilterInput
}

List Filter

List filters are generated for all nested enumerations.

public class User
{
    public string[] Roles { get; set; }

    public IEnumerable<Address> Addresses { get; set; }
}

public class Address
{
    public string Street { get; set; }

    public bool IsPrimary { get; set; }
}

public class Query
{
    [UseFiltering]
    public IQueryable<User> GetUsers([Service] IUserRepository repository)
        => repository.GetUsers();
}

SDL

type Query {
  users(where: UserFilterInput): [User]
}

input AddressFilterInput {
  and: [AddressFilterInput!]
  or: [AddressFilterInput!]
  street: StringOperationFilterInput
  isPrimary: BooleanOperationFilterInput
}

input BooleanOperationFilterInput {
  eq: Boolean
  neq: Boolean
}

input ListAddressFilterInput {
  all: AddressFilterInput
  none: AddressFilterInput
  some: AddressFilterInput
  any: Boolean
}

input ListStringOperationFilterInput {
  all: StringOperationFilterInput
  none: StringOperationFilterInput
  some: StringOperationFilterInput
  any: Boolean
}

input StringOperationFilterInput {
  and: [StringOperationFilterInput!]
  or: [StringOperationFilterInput!]
  eq: String
  neq: String
  contains: String
  ncontains: String
  in: [String]
  nin: [String]
  startsWith: String
  nstartsWith: String
  endsWith: String
  nendsWith: String
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  roles: ListStringOperationFilterInput
  addresses: ListAddressFilterInput
}

Filter Conventions

If you want to change the behavior filtering globally, you want to create a convention for your filters. The filter convention comes with a fluent interface that is close to a type descriptor.

Get Started

To use a filter convention you can extend FilterConvention and override the Configure method. Alternatively, you can directly configure the convention over the constructor argument. You then have to register your custom convention on the schema builder with AddConvention. By default a new convention is empty. To add the default behaviour you have to add AddDefaults.

public class CustomConvention : FilterConvention
{
    protected override void Configure(IFilterConventionDescriptor descriptor)
    {
        descriptor.AddDefaults();
    }
}

services.AddGraphQLServer()
    .AddConvention<IFilterConvention, CustomConvention>();
// or
services.AddGraphQLServer()
    .AddConvention<IFilterConvention>(new FilterConvention(x =>
        x.AddDefaults()))

Often you just want to extend the default behaviour of filtering. If this is the case, you can also use FilterConventionExtension

public class CustomConventionExtension : FilterConventionExtension
{
    protected override void Configure(IFilterConventionDescriptor descriptor)
    {
        // config
    }
}

services.AddGraphQLServer()
    .AddConvention<IFilterConvention, CustomConventionExtension>();
// or
services.AddGraphQLServer()
    .AddConvention<IFilterConvention>(new FilterConventionExtension(x =>
    {
        // config
    }));

Argument Name

With the convention descriptor, you can easily change the argument name of the FilterInputType.

Configuration

descriptor.ArgumentName("example_argument_name");

Result

SDL

type Query {
  users(example_argument_name: UserFilter): [User]
}

Binding of FilterTypes

FilterInputType's cannot just be registered on the schema. You have to bind them to the runtime type on the convention.

Configuration

public class UserFilterInput : FilterInputType<User>
{
    protected override void Configure(
        IFilterInputTypeDescriptor<User> descriptor)
    {
        descriptor.Field(x => x.Name).Description("This is the name");
    }
}

public class CustomStringOperationFilterInput : StringOperationFilterInput
{
    protected override void Configure(IFilterInputTypeDescriptor descriptor)
    {
        descriptor
            .Operation(DefaultFilterOperations.Equals)
            .Type<StringType>();
        descriptor
            .Operation(DefaultFilterOperations.NotEquals)
            .Type<StringType>();
    }
}

descriptor.BindRuntimeType<string, CustomStringOperationFilterInput >();
descriptor.BindRuntimeType<User, UserFilterInput>();

Result

SDL

type Query {
  users(where: UserFilterInput): [User]
}

type User {
  name: String!
}

input CustomStringOperationFilterInput {
  and: [CustomStringOperationFilterInput!]
  or: [CustomStringOperationFilterInput!]
  eq: String
  neq: String
}

input UserFilterInput {
  and: [UserFilterInput!]
  or: [UserFilterInput!]
  "This is the name"
  name: CustomStringOperationFilterInput
}

Extend FilterTypes

Instead of defining your own operation type, you can also just change the configuration of the built in ones. You can use Configure<TFilterType>() to alter the configuration of a type.

  descriptor.Configure<StringOperationFilterInput>(
    x => x.Operation(DefaultFilterOperations.Equals).Description("Equals"))

SDL

input StringOperationFilterInput {
  and: [StringOperationFilterInput!]
  or: [StringOperationFilterInput!]
  "Equals"
  eq: String
  neq: String
  contains: String
  ncontains: String
  in: [String]
  nin: [String]
  startsWith: String
  nstartsWith: String
  endsWith: String
  nendsWith: String
}

Last updated on 2021-08-10 by Tobias Tengler