How Can LINQ's `Contains()` Method Replace a `WHERE IN` Clause?

Where IN Clause in LINQ

When working with databases, you may encounter the need to use the WHERE IN clause to filter results based on multiple criteria. This can be easily achieved in LINQ (Language Integrated Query) using the Contains() method.

To illustrate, suppose you want to retrieve all states that belong to a specific list of country codes. Instead of manually splitting the country codes and looping through them as seen in the original code:

public List<State> Wherein(string listofcountrycodes)
{
    string[] countrycode = null;
    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;
}

You can simplify this process using the Contains() method:

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

This expression retrieves all states whose country codes are present in the countryCodes collection. The lambda expression (s => countryCodes.Contains(s.CountryCode)) evaluates to true for each state that matches the specified criteria, allowing you to filter the results accordingly.

The above is the detailed content of How Can LINQ's `Contains()` Method Replace a `WHERE IN` Clause?. For more information, please follow other related articles on the PHP Chinese website!