Single, SingleOrDefault, First and FirstOrDefault in LINQ

Single

• Returns the result only when predicate matches the collection that contains only one matching record.

    public List<string> Names = new List<string>() { "Jon", "Amber"};

    public string GetName()
    {
        return Names.Single(n=>n.Equals("Jon"));
    }

• Throws error if the collection contains more than one matching data or no matching data.

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.Single(n=>n.Contains("Jon"));
    }

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.Single(n=>n.Contains("ABC"));
    }

• Loops through all the data of the collection even if it found the match in collection which has impact on performance.

SingleOrDefault

• This is similar to the Single except returning default value when the specified condition not satisfied.

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.SingleOrDefault(n=>n.Contains("ABC"));
    }

• Returns the null(default of string type) instead of throwing error.

First

• Returns the result only when predicate matches the collection even that contains more than one matching record.

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.First(n=>n.Contains("Jon"));
    }

• Throws error if the collection contains no matching data.

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.First(n=>n.Contains("ABC"));
    }

• Will not loops through all the data of the collection once it found the match in collection thus making this is better than Single in terms of performance.

FirstOrDefault

• This is similar to the First except returning default value when the specified condition not satisfied.

    public List<string> Names = new List<string>() { "Jon", "Amber", "Depp Jon","Heard Amber" };

    public string GetName()
    {
        return Names.FirstOrDefault(n=>n.Contains("ABC"));
    }

• Returns the null(default of string type) instead of throwing error.