对数据库的异步操作

Question

I am building a WF application "Newsletter" to send emails to selected Email Groups which are created from this application and stored in a .sdf database which is SQL Server Compact Edition, built into Visual Studio 2012.

As of now I did this application running on Main thread, but this is not the approach that should be used with databases, I would like to do all operations on the database asynchronously. I have read about few approaches, but I never used them and am puzzled.

For ppl who are interested how DB and relations look like read square brackets beneath:

As of now there are 2 tables:

1. Emails (int UniqueID, string Email)
2. Groups (int ID, string Grupa)

PK in 1st table is UniqueID+Email and in 2nd ID+string , in 2nd table FK to table 1 is ID and it connects to UniqueID .

I am going to add 3rd table with ExistingGroups with 1 column ExstGroup and it will be related to table 2, where Grupa will be FK to ExistingGroups and this 3rd table will store names of all groups in our database and will be used to dynamically create checkboxes (stored in checkedListBox?) when application starts it will be triggerd in FormLoad event I suppose, correct me if I'm wrong

I would like to use ADO.net connected layer approach, so here are a few questions:

1. Where should i establish connection to database (conn.Open()), during Form_Load event? And should I check if this conn is open b4 attempting to execute any operation on DB?

2. Here is code snippet of taking Emails from DB and inserting it into hashset to pass those emails to SendingEmail function. How would you change it into asynchronous?

     // CheckedEmails is Form variable to store emails from groups which where checked on checkboxes. HashSet<string> CheckedEmails = new HashSet<string>(); private HashSet<string> ListOfEmails() { CheckedEmails.Clear(); Queue<string> checkBoxes = new Queue<string>(); if (IT_checkbox.Checked) //checking all checkboxes this way.. { checkBoxes.Enqueue(IT_checkbox.Text); } SqlCeCommand cmd = conn.CreateCommand(); while (checkBoxes.Count() != 0) { cmd.CommandText = string.Format("Select Email FROM Emails INNER JOIN Groups ON Emails.UniqueID=Groups.ID WHERE Groups.Grupa='{0}' ", checkBoxes.Dequeue()); SqlCeDataReader dr = cmd.ExecuteReader(); while (dr.Read()) { CheckedEmails.Add((string)dr["Email"]);//adding emails fromcheckedgroups } dr.Close(); } return CheckedEmails; } 

2A) Lets assume that this operation on DB is costly and takes some time, how would I prevent user from performing, this operation on DB many times, or other operations on DB (like adding new Emails) while this operation is in progress?

3.Can I use something to let user know that operation on DB is currently running, like some progress bar or changing mouse cursor to Loading? And How?

Thank you all for your help in advance, I tried to be as precise as I could, but if anything is not understandable please ask.

Answer 1

2）您可以使用异步和等待功能;）