CA1827: Do not use Count()/LongCount() when Any() can be used

Property	Value
Rule ID	CA1827
Title	Do not use Count()/LongCount() when Any() can be used
Category	Performance
Fix is breaking or non-breaking	Non-breaking
Enabled by default in .NET 8	As suggestion

Cause

The Count() or LongCount() method was used where the Any() method would be more efficient.

Rule description

This rule flags Count() and LongCount() LINQ method calls that are used to check if the collection has at least one element. These methods enumerate the entire collection to compute the count. The same check is faster with the Any() method as it avoids enumerating the collection.

Note

This rule is similar to CA1860: Avoid using 'Enumerable.Any()' extension method. However that rule suggests using the Count property, while this rule applies to the Linq Count() extension method.

How to fix violations

To fix a violation, replace the Count or LongCount method call with the Any method. For example, the following two code snippets show a violation of the rule and how to fix it:

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

class C
{
    public string M1(IEnumerable<string> list)
        => list.Count() != 0 ? "Not empty" : "Empty";

    public string M2(IEnumerable<string> list)
        => list.LongCount() > 0 ? "Not empty" : "Empty";
}

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

class C
{
    public string M1(IEnumerable<string> list)
        => list.Any() ? "Not empty" : "Empty";

    public string M2(IEnumerable<string> list)
        => list.Any() ? "Not empty" : "Empty";
}

Tip

A code fix is available for this rule in Visual Studio. To use it, position the cursor on the violation and press Ctrl+. (period). Choose Do not use Count() or LongCount() when Any() can be used from the list of options that's presented.

When to suppress warnings

It's safe to suppress a violation of this rule if you're not concerned about the performance impact from unnecessary collection enumeration to compute the count.

Suppress a warning

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

#pragma warning disable CA1827
// The code that's violating the rule is on this line.
#pragma warning restore CA1827

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

[*.{cs,vb}]
dotnet_diagnostic.CA1827.severity = none

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

Related rules

• CA1826: Use property instead of Linq Enumerable method
• CA1828: Do not use CountAsync/LongCountAsync when AnyAsync can be used
• CA1829: Use Length/Count property instead of Enumerable.Count() method
• CA1860: Avoid using 'Enumerable.Any()' extension method

See also

• Performance rules