Add support for query notifications

[maxhauser]

Added SetQueryNotification method to MssqlStmt. Parameter semantics are the same as in new SqlNotificationRequest(userData,options,timeout).

[denisenkom]

Can you add a test for this feature?

[bbigras]

I'm also interested to see how it works. I don't know how to use SetQueryNotification(). I don't know how to get MssqlStmt from sql.DB or sql.Stmt.

@maxhauser do you use this in production? Does it work well?

[bbigras]

@denisenkom any idea how to use this?

[maxhauser]

I used that just for a proof of concept but it did not made it into production. The use of the SetQueryNotification() method is similar to the SqlNotificationRequest described here.

To get a MssqlStmt you have to cast the Stmt that you get from Prepare() like this:

stmt, err := cn.Prepare("SELECT Name FROM dbo.Test")
if err != nil {
    panic(err)
}

sqlstmt := stmt.(*mssql.MssqlStmt)
sqlstmt.SetQueryNotification("ABC", "service=WebCacheNotifications", time.Hour)

Change notifications are then posted to the specified service broker service.

For more information about query notifications and how to set up the service broker that is a good start.

[bbigras]

To get a MssqlStmt you have to cast the Stmt that you get from Prepare()

I tried that but I had an invalid type assertion error.

The following code give this error, I wonder if something changed in go-mssqldb or Go since the last time you tried it.

.\main.go:26: invalid type assertion: stmt.(*mssql.MssqlStmt) (non-interface type *sql.Stmt on left)`

package main

import (
    "database/sql"
    "time"

    _ "github.com/maxhauser/go-mssqldb"
)

func main() {
    cn, err := sql.Open("mssql", sqlStr)
    if err != nil {
        panic(err)
    }
    defer cn.Close()

    stmt, err := cn.Prepare("SELECT Name FROM dbo.Test")
    if err != nil {
        panic(err)
    }

    sqlstmt := stmt.(*mssql.MssqlStmt)
    sqlstmt.SetQueryNotification("ABC", "service=WebCacheNotifications", time.Hour)
}

[maxhauser]

Sorry, I forgot to mention that you have to have a MssqlDriver connection. Try to open the connection directly with the mssql driver, like that:

 import mssql "github.com/maxhauser/go-mssqldb"

...

 mssqldriver := &mssql.MssqlDriver{}
 cn, err := mssqldriver.Open(connectionstring)

[bbigras]

Thanks, it worked.

I'm not sure if I do the right thing or maybe query notifications doesn't work the way I think.

The following code executes the query, prints the output and exits. How do I get the notification? I was thinking that maybe the query would block until there's a change.

    stmt, err := cn.Prepare("SELECT test FROM dbo.test;")
    if err != nil {
        panic(err)
    }

    sqlstmt := stmt.(*mssql.MssqlStmt)
    sqlstmt.SetQueryNotification("ABC", "service=WebCacheNotifications", time.Hour)

    rows, errQuery := sqlstmt.Query(nil)
    if errQuery != nil {
        panic(errQuery)
    }
    defer rows.Close()

    result := make([]driver.Value, 1)
    if err := rows.Next(result); err != nil {
        panic(err)
    }
    fmt.Println(result)

[bbigras]

Anyone?

[maxhauser]

Change notifications are posted to the specified service broker service.
So you can listen for notifications with RECEIVE on a second connection.
For more information about query notifications and how to set up the service broker that is a good start.

[denisenkom]

merged, thanks!