.mdf Database don't change anything [duplicate]

This question already has an answer here:

• Why saving changes to a database fails? 2 answers

I'm trying to make an desktop app to be portable with a .mdf database, and when i make changes to the database, IT CHANGES, but when i close and start the app again, database is empty, it not saves data as it should.

I'm using this class to interact with the database:

class SQL
{
    SqlConnection connection;
    SqlCommand command;
    SqlDataAdapter data;
    DataTable dtResult;

    public SqlConnection Ligar()
    {
        connection = new SqlConnection(ConfigurationManager.ConnectionStrings["DC.Properties.Settings.DCConnectionString"].ConnectionString);
        connection.Open();
        return connection;
    }
    public DataTable Execute(string query)
    {
        using (var conn = Ligar())
        {
            dtResult = new DataTable();
            data = new SqlDataAdapter(query, conn);
            data.Fill(dtResult);
            connection.Close();
        }
        return dtResult;
    }
    public void Query(string query)
    {
        try
        {
            using (var conn = Ligar())
            {
                command = new SqlCommand(query, conn);
                command.ExecuteNonQuery();
                connection.Close();
            }
        }
        catch (Exception msg) 
        {  
        }
    }

APP SETTINGS:

    <connectionStrings>
        <add name="DC.Properties.Settings.DCConnectionString" 
            connectionString="Data Source=(LocalDB)\v11.0;;AttachDbFilename=|DataDirectory|\DC.mdf;Integrated Security=True;"
            providerName="System.Data.SqlClient" />
    </connectionStrings>