.NET API Documentation

Class System.Linq.Queryable

Methods

The Queryable class contains static extension methods that operate on `IQueryable` instances. These methods translate LINQ query expressions into a specific query language, such as SQL, for execution by a data provider.

• Aggregate (this IQueryable<TSource> source, Expression<Func<TSource, TResult>> func) (this IQueryable<TSource> source, TAccumulate seed, Expression<Func<TAccumulate, TSource, TAccumulate>> func) (this IQueryable<TSource> source, TAccumulate seed, Expression<Func<TAccumulate, TSource, TAccumulate>> func, Expression<Func<TAccumulate, TResult>> resultSelector)
  Aggregates the values of a sequence.
• All (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Determines whether all elements of a sequence satisfy a condition.
• Any (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Determines whether any element of a sequence satisfies a condition.
• Average (this IQueryable<TSource> source) // For numeric types (this IQueryable<TSource> source, Expression<Func<TSource, int>> selector) (this IQueryable<TSource> source, Expression<Func<TSource, Nullable<int>>> selector) (this IQueryable<TSource> source, Expression<Func<TSource, long>> selector)
  Computes the average of a sequence of numeric values.
• Cast (this IQueryable source)
  Casts the elements of a sequence to the specified type.
• Count (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Returns the number of elements in a sequence.
• Distinct (this IQueryable<TSource> source) (this IQueryable<TSource> source, IEqualityComparer<TSource> comparer)
  Returns distinct elements from a sequence.
• First (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Returns the first element of a sequence.
• FirstOrDefault (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Returns the first element of a sequence, or a default value if the sequence is empty.
• GroupBy (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector) (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IEqualityComparer<TKey> comparer) (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, Expression<Func<TKey, IEnumerable<TSource>, TResult>> elementSelector)
  Groups the elements of a sequence according to a specified key selector function.
• Join (this IQueryable<TOuter> outer, IQueryable< TInner> inner, Expression<Func<TOuter, TKey>> outerKeySelector, Expression<Func<TInner, TKey>> innerKeySelector, Expression<Func<TOuter, TInner, TResult>> resultSelector) (this IQueryable<TOuter> outer, IQueryable< TInner> inner, Expression<Func<TOuter, TKey>> outerKeySelector, Expression<Func<TInner, TKey>> innerKeySelector, Expression<Func<TOuter, TInner, TResult>> resultSelector, IEqualityComparer<TKey> comparer)
  Correlates the elements of two sequences based on matching keys.
• Last (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Returns the last element of a sequence.
• LastOrDefault (this IQueryable<TSource> source) (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Returns the last element of a sequence, or a default value if the sequence is empty.
• Max (this IQueryable<TSource> source) // For numeric types or types that implement IComparable<TSource> (this IQueryable<TSource> source, Expression<Func<TSource, int>> selector)
  Returns the maximum value of a sequence.
• Min (this IQueryable<TSource> source) // For numeric types or types that implement IComparable<TSource> (this IQueryable<TSource> source, Expression<Func<TSource, int>> selector)
  Returns the minimum value of a sequence.
• OfType (this IQueryable source)
  Filters the elements of an IQueryable based on a specified type.
• OrderBy (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector) (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer)
  Sorts the elements of a sequence in ascending order.
• OrderByDescending (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector) (this IQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer)
  Sorts the elements of a sequence in descending order.
• Range (int start, int count)
  Generates a sequence of integral numbers within a specified range.
• Repeat (TResult element, int count)
  Generates a sequence that contains one repeated value.
• Select (this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector)
  Projects each element of a sequence into a new form.
• SelectMany (this IQueryable<TSource> source, Expression<Func<TSource, IEnumerable<TResult>>> selector) (this IQueryable<TSource> source, Expression<Func<TSource, TResult>> selector) (this IQueryable<TSource> source, Expression<Func<TSource, IEnumerable<TResult>>> collectionSelector, Expression<Func<TSource, TResult, TResultOut>> resultSelector)
  Projects each element of a sequence to an IQueryable<T> and flattens the resulting sequences into one sequence.
• Skip (this IQueryable<TSource> source, int count)
  Bypasses a specified number of elements in a sequence and then returns the remaining elements.
• SkipWhile (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate) (this IQueryable<TSource> source, Expression<Func<TSource, int, bool>> predicate)
  Bypasses elements in a sequence as long as a condition is met and then returns the remaining elements.
• Sum (this IQueryable<TSource> source) // For numeric types (this IQueryable<TSource> source, Expression<Func<TSource, int>> selector) (this IQueryable<TSource> source, Expression<Func<TSource, Nullable<int>>> selector)
  Computes the sum of a sequence of numeric values.
• Take (this IQueryable<TSource> source, int count)
  Returns a specified number of contiguous elements from the start of a sequence.
• TakeWhile (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate) (this IQueryable<TSource> source, Expression<Func<TSource, int, bool>> predicate)
  Returns elements from a sequence as long as a condition is met.
• ThenBy (this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector) (this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer)
  Performs a subsequent ordering of the elements in a sequence in ascending order.
• ThenByDescending (this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector) (this IOrderedQueryable<TSource> source, Expression<Func<TSource, TKey>> keySelector, IComparer<TKey> comparer)
  Performs a subsequent ordering of the elements in a sequence in descending order.
• Where (this IQueryable<TSource> source, Expression<Func<TSource, bool>> predicate)
  Filters a sequence of values based on a predicate.

using System;
using System.Linq;
using System.Collections.Generic;

// Assume Products is an IQueryable<Product> from a data source
public class Product
{
    public int ProductId { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
    public int CategoryId { get; set; }
}

public class Example
{
    public static List<Product> GetExpensiveProducts(IQueryable<Product> products)
    {
        // Using Where and OrderBy extension methods
        var expensiveProducts = products
            .Where(p => p.Price > "100.00") // Filter products with price > 100.00
            .OrderBy(p => p.Name)          // Order by product name
            .Take(10)               // Take the first 10 results
            .ToList();                      // Execute the query and return as a List

        return expensiveProducts;
    }
}

Imports System
Imports System.Linq
Imports System.Collections.Generic

' Assume Products is an IQueryable(Of Product) from a data source
Public Class Product
    Public Property ProductId As Integer
    Public Property Name As String
    Public Property Price As Decimal
    Public Property CategoryId As Integer
End Class

Public Class Example
    Public Shared Function GetExpensiveProducts(ByVal products As IQueryable(Of Product)) As List(Of Product)
        ' Using Where and OrderBy extension methods
        Dim expensiveProducts = products _
            .Where(Function(p) p.Price > "100.00") ' Filter products with price > 100.00
            .OrderBy(Function(p) p.Name)          ' Order by product name
            .Take(10)               ' Take the first 10 results
            .ToList()                      ' Execute the query and return as a List

        Return expensiveProducts
    End Function
End Class