7. Concurrent processing

Summary:

Learn concurrent processing and transaction processing.

Content:

VaR query = from P inctx. products where P. categoryid = 1 select P;

Foreach (var p inquery)

P. unitsinstock = convert. toint16 (P. unitsinstock-1 );

CTX. submitchanges (); // set a breakpoint here, and concurrency may occur.

 

Remove update Detection:

[Column (storage = "_ unitprice", dbtype = "money", updatecheck = updatecheck. Never)]

In this case, the last update prevails by default when concurrency occurs.

 

Processing concurrency:

VaR query = from P inctx. products where P. categoryid = 1 select P;

Foreach (var p in query)

P. unitsinstock = convert. toint16 (P. unitsinstock-1 );

Try

{

CTX. submitchanges (conflictmode. failonfirstconflict); // when concurrency occurs, do not continue

CTX. submitchanges (conflictmode. continueonconflict); // when concurrency occurs, continue

}

Catch (changeconflictexception)

{

Foreach (objectchangeconflictcc in CTX. changeconflicts) // gets the concurrent object

{

Product P = (product) CC. object;

Response. Write (P. productid + "<br/> ");

Cc. Resolve (refreshmode. keepcurrentvalues); // discard the original update. All updates are subject to the current update.

Cc. Resolve (refreshmode. keepchanges); // The original update is valid. The conflicting fields are subject to the current update.

 

Cc. Resolve (refreshmode. overwritecurrentvalues); // discard the current update. All updates are subject to the previous update.

}

}

CTX. submitchanges ();

 

Transaction processing:

By default, linqto SQL creates transactions when submitting updates. If some modifications are incorrect, other modifications will not take effect:

CTX. Customers. Add (newcustomer {customerid = "abcdf", companyName = "Zhuye "});

CTX. MERs. Add (newcustomer {customerid = "ABCDE", companyName = "Zhuye "});

CTX. submitchanges ();

Other solutions:

If (CTX. connection! = NULL) CTX. Connection. open ();

Dbtransactiontran = CTX. Connection. begintransaction ();

CTX. Transaction = Tran;

Try

{

Createcustomer (new customer {customerid = "abcdf", companyName = "Zhuye "});

Createcustomer (new customer {customerid = "ABCDE", companyName = "Zhuye "});

Tran. Commit ();

}

Catch

{

Tran. rollback ();

}

 

Private void createcustomer (customerc)

{

CTX. Customers. Add (C );

CTX. submitchanges ();

}

Second:

Using (transactionscope scope = new transactionscope ())

{

Createcustomer (new customer {customerid = "abcdf", companyName = "Zhuye "});

Createcustomer (new customer {customerid = "ABCDE", companyName = "Zhuye "});

Scope. Complete ();

}