// Adds random employee data to the database by using dataflow.
// This method is similar to AddEmployees except that it uses batching
// to add multiple employees to the database at a time.
static void AddEmployeesBatched(string connectionString, int batchSize, int count)
{
// Create a BatchBlock<Employee> that holds several Employee objects and
// then propagates them out as an array.
BatchBlock <Employee> batchEmployees = new BatchBlock <Employee>(batchSize);
// Create an ActionBlock<Employee[]> object that adds multiple
// employee entries to the database.
ActionBlock <Employee[]> insertEmployees = new ActionBlock <Employee[]>(a =>
{
DatabaseUtilities.InsertEmployees(a, connectionString, "AddEmployeesBatched");
});
// Link the batch block to the action block.
batchEmployees.LinkTo(insertEmployees);
// When the batch block completes, set the action block also to complete.
batchEmployees.Completion.ContinueWith(obj =>
{
insertEmployees.Complete();
});
// Post several random Employee objects to the batch block.
PostRandomEmployees(batchEmployees, count);
// Set the batch block to the completed state and wait for
// all insert operations to complete.
batchEmployees.Complete();
insertEmployees.Completion.Wait();
}
// Adds random employee data to the database by using dataflow.
static void AddEmployees(string connectionString, int count)
{
// Create an ActionBlock<Employee> object that adds a single
// employee entry to the database.
ActionBlock <Employee> insertEmployee = new ActionBlock <Employee>(e =>
{
DatabaseUtilities.InsertEmployees(new[] { e }, connectionString, "AddEmployees");
});
// Post several random Employee objects to the dataflow block.
PostRandomEmployees(insertEmployee, count);
// Set the dataflow block to the completed state and wait for
// all insert operations to complete.
insertEmployee.Complete();
insertEmployee.Completion.Wait();
}
public static void Run()
{
// Create a connection string for accessing the database.
// The connection string refers to the temporary database location.
string connectionString = string.Format(@"Data Source={0}", scratchDatabase);
// Create a Stopwatch object to time database insert operations.
Stopwatch stopwatch = new Stopwatch();
// Start with a clean database file by copying the source database to
// the temporary location.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple insert operations without batching.
Console.WriteLine("Demonstrating non-batched database insert operations...");
Console.WriteLine("Original size of Employee table: {0}.", DatabaseUtilities.GetEmployeeCount(connectionString));
stopwatch.Start();
AddEmployees(connectionString, insertCount);
stopwatch.Stop();
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", DatabaseUtilities.GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);
Console.WriteLine();
// Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple insert operations, this time with batching.
Console.WriteLine("Demonstrating batched database insert operations...");
Console.WriteLine("Original size of Employee table: {0}.", DatabaseUtilities.GetEmployeeCount(connectionString));
stopwatch.Restart();
AddEmployeesBatched(connectionString, insertBatchSize, insertCount);
stopwatch.Stop();
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", DatabaseUtilities.GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);
Console.WriteLine();
// Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple retrieval operations with error reporting.
Console.WriteLine("Demonstrating batched join database select operations...");
// Add a small number of employees to the database.
AddEmployeesBatched(connectionString, insertBatchSize, 16);
// Query for random employees.
GetRandomEmployees(connectionString, insertBatchSize, 10);
}
// Displays information about several random employees to the console.
static void GetRandomEmployees(string connectionString, int batchSize, int count)
{
// Create a BatchedJoinBlock<Employee, Exception> object that holds
// both employee and exception data.
BatchedJoinBlock <Employee, Exception> selectEmployees = new BatchedJoinBlock <Employee, Exception>(batchSize);
// Holds the total number of exceptions that occurred.
int totalErrors = 0;
// Create an action block that prints employee and error information
// to the console.
ActionBlock <Tuple <IList <Employee>, IList <Exception> > > printEmployees =
new ActionBlock <Tuple <IList <Employee>, IList <Exception> > >(data =>
{
// Print information about the employees in this batch.
Console.WriteLine("Received a batch...");
foreach (Employee e in data.Item1)
{
Console.WriteLine("Last={0} First={1} ID={2}",
e.FirstName, e.LastName, e.EmployeeID);
}
// Print the error count for this batch.
Console.WriteLine("There were {0} errors in this batch...",
data.Item2.Count);
// Update total error count.
totalErrors += data.Item2.Count;
});
// Link the batched join block to the action block.
selectEmployees.LinkTo(printEmployees);
// When the batched join block completes, set the action block also to complete.
selectEmployees.Completion.ContinueWith(delegate { printEmployees.Complete(); });
// Try to retrieve the ID for several random employees.
Console.WriteLine("Selecting random entries from Employees table...");
for (int i = 0; i < count; i++)
{
try
{
// Create a random employee.
Employee e = Employee.Random();
// Try to retrieve the ID for the employee from the database.
e.EmployeeID = DatabaseUtilities.GetEmployeeID(e.LastName, e.FirstName, connectionString);
// Post the Employee object to the Employee target of
// the batched join block.
selectEmployees.Target1.Post(e);
}
catch (NullReferenceException e)
{
// GetEmployeeID throws NullReferenceException when there is
// no such employee with the given name. When this happens,
// post the Exception object to the Exception target of
// the batched join block.
selectEmployees.Target2.Post(e);
}
}
// Set the batched join block to the completed state and wait for
// all retrieval operations to complete.
selectEmployees.Complete();
printEmployees.Completion.Wait();
// Print the total error count.
Console.WriteLine("Finished. There were {0} total errors.", totalErrors);
}
