Learning Objectives

• Define the First() method in LINQ.
• Define the FirstOrDefault() method in LINQ.
• Understand how to choose between First() and FirstOrDefault().

Prerequisites

• Basic familiarity with the C# programming language.
• A brief understanding of LINQ concepts.

Getting Started

This article illustrates two distinct methods, First() and FirstOrDefault(), for retrieving the first element from a data sequence.

What is the First() Method?

The First() method is designed to retrieve the first element of a sequence, with an optional filter condition specified via lambda expressions.

The general syntax is:

First(x => x.columnName == value);

However, it may result in an InvalidOperationException under the following circumstances:

• When no elements fulfill the expression condition.
• When the source is null.

Recommendation: Ensure that the sequence contains at least one element before calling the First() method.

Example: Consider a table UserDetails with columns (ID, Name) and values ranging from 1 to 10.

var result = dc.UserDetails.First(x => x.ID == 1);

// Output: ID: 1, Name: Manish Dubey

If we attempt to retrieve data for an ID=13, which does not exist in the UserDetails table, it will throw an InvalidOperationException.

var result = dc.UserDetails.First(x => x.ID == 13);

// Throws InvalidOperationException: Sequence contains no elements

What is the FirstOrDefault() Method?

The FirstOrDefault() method functions similarly to First(), but it returns a default value if no elements match the specified conditional expression. The default value is null for reference types and 0 for value types.

The general syntax is:

FirstOrDefault(x => x.columnName == value);

Example: Again, using the UserDetails table with columns (ID, Name) and values from 1 to 10.

var result = dc.UserDetails.FirstOrDefault(x => x.ID == 1);

// Output: ID: 1, Name: Manish Dubey

If we attempt to fetch data for ID=13, which does not exist in the UserDetails table, it will return a default value of null.

var result = dc.UserDetails.FirstOrDefault(x => x.ID == 13);

// Output: null

Choosing Between First() and FirstOrDefault()

Use the First() method when it's essential that the result is not empty. Opt for the FirstOrDefault() method when you need to incorporate empty checks into your logic for the sequence.

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