How Can I Optimize WHERE IN Queries in LINQ for Better Performance?

Using the WHERE IN Clause in LINQ to Improve Performance

When working with large datasets, the efficiency of your code becomes crucial. In SQL Server, the WHERE IN clause allows you to filter records based on multiple values within a specified range. This can significantly improve query performance compared to using multiple OR conditions.

LINQ (Language-Integrated Query) provides a similar functionality for C# developers. However, the basic syntax may not offer optimal performance. In this article, we present a more efficient approach to performing a WHERE IN query in LINQ.

Consider the following code block:

public List<State> Wherein(string listofcountrycodes)
{
    string[] countrycode = listofcountrycodes.Split(',');
    List<State> statelist = new List<State>();

    for (int i = 0; i < countrycode.Length; i++)
    {
        _states.AddRange(
             from states in _objdatasources.StateList()
             where states.CountryCode == countrycode[i].ToString()
             select new State
             {
                StateName  = states.StateName                    

             });
    }
    return _states;
}

This code performs a series of queries for each value in the listofcountrycodes array. While it gets the job done, it's not as efficient as it could be.

To improve performance, we can use the following concise LINQ expression:

dataSource.StateList.Where(s => countryCodes.Contains(s.CountryCode))

In this expression, we use the Contains() method to check if the CountryCode of each State in StateList is present in the countryCodes array. By combining all the conditions into a single expression, we avoid the performance overhead of executing multiple queries.

This optimized approach results in a significant improvement in query speed, particularly when working with large datasets. It provides a cleaner and more concise way to perform WHERE IN operations in LINQ, making your code more efficient and easier to maintain.

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