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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Collections;
using System.Collections.Generic;
using System.Linq.Expressions;
namespace System.Linq
{
/// <summary>
/// Provides functionality to evaluate queries against a specific data source wherein the type of the data is not specified.
/// </summary>
public interface IQueryable : IEnumerable
{
/// <summary>
/// Gets the expression tree that is associated with the instance of <see cref="IQueryable"/>.
/// </summary>
Expression Expression { get; }
/// <summary>
/// Gets the type of the element(s) that are returned when the expression tree associated with this instance of <see cref="IQueryable"/> is executed.
/// </summary>
Type ElementType { get; }
/// <summary>
/// Gets the query provider that is associated with this data source.
/// </summary>
IQueryProvider Provider { get; }
}
/// <summary>
/// Provides functionality to evaluate queries against a specific data source wherein the type of the data is known.
/// </summary>
/// <typeparam name="T">The type of the data in the data source.</typeparam>
public interface IQueryable<out T> : IEnumerable<T>, IQueryable
{
}
/// <summary>
/// Defines methods to create and execute queries that are described by an <see cref="IQueryable"/> object.
/// </summary>
/// <remarks>
/// The <see cref="IQueryProvider"/> interface is intended for implementation by query providers.
/// </remarks>
public interface IQueryProvider
{
/// <summary>
/// Constructs an <see cref="IQueryable"/> object that can evaluate the query represented by a specified expression tree.
/// </summary>
/// <param name="expression">An expression tree that represents a LINQ query.</param>
/// <returns>An <see cref="IQueryable"/> that can evaluate the query represented by the specified expression tree.</returns>
/// <remarks>
/// The CreateQuery method is used to create new <see cref="IQueryable"/> objects, given an expression tree. The query that is represented by the returned object is associated with a specific LINQ provider.
/// Several of the standard query operator methods defined in Queryable, such as OfType{TResult} and Cast{TResult}, call this method. They pass it a <see cref="MethodCallExpression"/> that represents a LINQ query.
/// </remarks>
IQueryable CreateQuery(Expression expression);
/// <summary>
/// Constructs an <see cref="IQueryable{T}"/> object that can evaluate the query represented by a specified expression tree.
/// </summary>
/// <param name="expression">An expression tree that represents a LINQ query.</param>
/// <returns>An <see cref="IQueryable{T}"/> that can evaluate the query represented by the specified expression tree.</returns>
/// <remarks>
/// The <see cref="CreateQuery{TElement}"/> method is used to create new <see cref="IQueryable{T}"/> objects, given an expression tree. The query that is represented by the returned object is associated with a specific LINQ provider.
/// Most of the Queryable standard query operator methods that return enumerable results call this method.They pass it a <see cref="MethodCallExpression"/> that represents a LINQ query.
/// </remarks>
IQueryable<TElement> CreateQuery<TElement>(Expression expression);
/// <summary>
/// Executes the query represented by a specified expression tree.
/// </summary>
/// <param name="expression">An expression tree that represents a LINQ query.</param>
/// <returns>The value that results from executing the specified query.</returns>
/// <remarks>
/// The <see cref="Execute"/> method executes queries that return a single value (instead of an enumerable sequence of values). Expression trees that represent queries that return enumerable results are executed when their associated <see cref="IQueryable"/> object is enumerated.
/// </remarks>
object Execute(Expression expression);
/// <summary>
/// Executes the strongly-typed query represented by a specified expression tree.
/// </summary>
/// <typeparam name="TResult">The type of the value that results from executing the query.</typeparam>
/// <param name="expression">An expression tree that represents a LINQ query.</param>
/// <returns>The value that results from executing the specified query.</returns>
/// <remarks>
/// The <see cref="Execute{TElement}"/> method executes queries that return a single value (instead of an enumerable sequence of values). Expression trees that represent queries that return enumerable results are executed when the <see cref="IQueryable{T}"/> object that contains the expression tree is enumerated.
/// The Queryable standard query operator methods that return singleton results call <see cref="Execute{TElement}"/>. They pass it a <see cref="MethodCallExpression"/> that represents a LINQ query.
/// </remarks>
TResult Execute<TResult>(Expression expression);
}
/// <summary>
/// Represents the result of a sorting operation.
/// </summary>
public interface IOrderedQueryable : IQueryable
{
}
/// <summary>
/// Represents the result of a sorting operation.
/// </summary>
/// <typeparam name="T">The type of the content of the data source.</typeparam>
public interface IOrderedQueryable<out T> : IQueryable<T>, IOrderedQueryable
{
}
}