I am using the following C# code to establish a SQL connect to a SQL
database file:

// connection string

// attach a SQL database file to a local SQL server express instance

string _connectionString = @"Server=.\SQLExpress; AttachDbFilename=C:
\BalanceDatabase_1.mdf; Trusted_Connection=Yes; User Instance=True";

// using System.Data.SqlClient;

SqlConnection _sqlConnection = new SqlConnection(_connectionString);

// open the connection

_sqlConnection.Open();

// do something

// close the connection

_sqlConnection.Close();

So far, the connection works fine.

However, next, I want to copy the database file to another folder. So
the following codes:

// source database file name

string sourceDatabaseFileName = @"C:\BalanceDatabase_1.mdf";

// target database file name
string targetDatabaseFileName = @"D:\BalanceDatabase_1.mdf";

// copy database file

System.IO.File.Copy(sourceDatabaseFileName, targetDatabaseFileName,
true);

Then the program came with runtime exception: "IOException was
unhandled: The process cannot access the file 'C:
\BalanceDatabase_1.mdf' because it is being used by another process."

Is it because the database file was sill attached to the local SQL
Server express instance? What can I do to bypass this problem? Detach
the database file? or dispose the local SQL Server express instance?

Many thanks indeed!