.Net Using Transactions with Prepared Statements for SqlClient - sql-server

Question

I'm trying to implement Transactions for a script but I've run into a strange issue.
When I attempt to run a Prepared SQL Statement inside of a Transaction it is failing because it says that it needs a Transaction when the connection is assigned.
How does this work with Prepared Statements though because I intend to have multiple Transactions all using the same Prepared Statements.
My code is as follows
class dbTest {
public static SqlConnection db;
public static SqlCommand query;
static void Main(string[] args) {
db = connect();
prepare();
transaction01();
transaction02();
transaction03();
}
public static void prepare() {
query = new SqlCommand("select id from table where id = 1 for update", db);
query.Prepare();
}
public static void transaction01() {
SqlTransaction trans = db.BeginTransaction("Trn01");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
public static void transaction02() {
SqlTransaction trans = db.BeginTransaction("Trn02");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
public static void transaction03() {
SqlTransaction trans = db.BeginTransaction("Trn03");
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}
}
How do I assign the Transaction to an existing Prepared Statement?
UPDATE
Changed the above code to better show the issue. The SQL is prepared once but I will be using it for multiple Transactions (or at least I want to)
UPDATE AGAIN
I have marked an answer below as the correct one because it looks like the best way to achieve this but for my needs in this very small example using query.Transaction got it working
public static void transaction01() {
SqlTransaction trans = db.BeginTransaction("Trn01");
query.Transaction = trans; // this line fixed it
SqlDataReader result = query.ExecuteReader();
while(result.Read()) { Console.WriteLine(result["id"]); }
result.Close();
trans.Commit();
}

Answer 1

When working with the SqlTransaction, you must set the SqlCommand.Transaction explicitly, even though enlisting in the current transaction is not optional in SQL Server.
select ... for update is not valid SQL Server syntax, instead use UPDLOCK to read a table and retain a restrictive lock for the duration of the transaction. EG
select id from table with (updlock) where id = 1
When I attempt to run a Prepared SQL Statement
It's rarely useful to use prepared statements with SQL Server. Query plan caching happens automatically even without it, and it really just reduces the size of the request on the network when you are executing a SqlCommand many times with differing parameters.
But a prepared SqlCommand is still bound to a single SqlConnection, which typically has a short lifetime, minimizing the potential benefits of preparing the SqlCommand.

Answer 2

You need to set the SqlCommand.Transaction to your transaction object.
it is not necessary with SQL Server to prepare the statement. Just keep executing.
Note also, as you can see in this post, that you must correctly dispose all DB objects.
Here is your code cleaned up:
class dbTest {
// DO NOT cache connection object
static void Main(string[] args) {
using(var db = connect())
using(var comm = GetCommand(db))
{
transaction01(comm);
transaction02(comm);
transaction03(comm);
}
}
public static SqlCommand GetCommand(SqlConnection conn) {
return new SqlCommand("select id from table with (updlock) where id = 1", conn);
}
public static void transaction01(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn01"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
public static void transaction02(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn02"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
public static void transaction03(SqlCommand comm) {
using(SqlTransaction trans = comm.Connection.BeginTransaction("Trn03"))
{
comm.Transaction = trans;
using(SqlDataReader result = query.ExecuteReader())
while(result.Read()) { Console.WriteLine(result["id"]); }
trans.Commit();
} // no need to close, using will sort that out
}
}