.First() vs. .FirstOrDefault() in LINQ: When Should I Use Each?

Usage scenarios of First() and FirstOrDefault() in LINQ

LINQ's .First() and .FirstOrDefault() methods are functionally similar but behave slightly differently. Let’s dig into the scenarios where each method is suitable.

When to use .First()

Use .First() if you are sure that the sequence will always contain at least one element. It will return the first matching element. If no matching element is found, an "InvalidOperationException" exception will be thrown. This method is suitable when an empty sequence is an exception.

When to use .FirstOrDefault()

Use .FirstOrDefault() if the sequence may be empty or is expected to be empty. If there is a matching element, it returns the first matching element; otherwise, it returns the default value for the element type. This method should be used when an empty sequence is a valid case.

When to use .Take(1)

The

.Take(1) method is similar to .First(), but with one key difference. It does not return the element itself, but a sequence containing exactly one element. This distinction becomes important when dealing with sequences of value types.

Example

Consider the following sequence:

<code class="language-csharp">var list = new List<int> { 1, 2, 3 };</code>

Use .First():

<code class="language-csharp">int result = list.Where(x => x % 2 == 0).First();</code>

Since there is an even number (2) in the sequence, this code will return the value 2. If there is no even number, an exception will be thrown.

Use .FirstOrDefault():

<code class="language-csharp">int result = list.Where(x => x % 2 == 4).FirstOrDefault();</code>

In this case, no even number matches the predicate, so .FirstOrDefault() returns the default value of an integer, which is 0.

Use .Take(1):

<code class="language-csharp">var result = list.Where(x => x % 2 == 0).Take(1);</code>

This code returns a sequence containing the single element 2.

The above is the detailed content of .First() vs. .FirstOrDefault() in LINQ: When Should I Use Each?. For more information, please follow other related articles on the PHP Chinese website!