Simplify LINQ expression (IDE0120)

Property	Value
Rule ID	IDE0120
Title	Simplify LINQ expression
Category	Style
Subcategory	Unnecessary code rules (expression-level preferences)
Applicable languages	C# and Visual Basic

Overview

This rule flags overly complex LINQ expressions, specifically expressions that call xref:System.Linq.Enumerable.Where%60%601(System.Collections.Generic.IEnumerable{%60%600},System.Func{%60%600,System.Int32,System.Boolean})?displayProperty=nameWithType followed by one of the following methods:

xref:System.Linq.Enumerable.Any%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.Count%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.First%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.FirstOrDefault%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.Last%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.LastOrDefault%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.Single%60%601(System.Collections.Generic.IEnumerable{%60%600})
xref:System.Linq.Enumerable.SingleOrDefault%60%601(System.Collections.Generic.IEnumerable{%60%600})

Such expressions can be simplified by removing the call to xref:System.Linq.Enumerable.Where%60%601(System.Collections.Generic.IEnumerable{%60%600},System.Func{%60%600,System.Int32,System.Boolean}) and instead calling an overload of Any(), Count(), First(), FirstOrDefault(), Last(), LastOrDefault(), Single, or SingleOrDefault() that accepts a predicate function to filter the elements.

Options

This rule has no associated code-style options.

Example

// Code with violations.
IEnumerable<string> words = new List<string> { "hello", "world", "!" };
var result = words.Where(x => x.Equals("hello")).Any();

// Fixed code.
IEnumerable<string> words = new List<string> { "hello", "world", "!" };
var result = words.Any(x => x.Equals("hello"));

Suppress a warning

If you want to suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable IDE0120
// The code that's violating the rule is on this line.
#pragma warning restore IDE0120

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.IDE0120.severity = none

To disable all of the code-style rules, set the severity for the category Style to none in the configuration file.

[*.{cs,vb}]
dotnet_analyzer_diagnostic.category-Style.severity = none

For more information, see How to suppress code analysis warnings.

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