Entity Framework 4.0: How to see SQL statements for SaveChanges method

Question

I used to use the context.Log for tracing LINQ to SQL generated SQL Statements as shown in Sql Server Query Visualizer – Cannot see generated SQL Query

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Answer 1

Expanding on Nate's answer for EF6, the NLogCommandInterceptor seen in Logging and Intercepting Database Operations only shows the CommandText.

If there was some particular parameter value that caused that commandText to fail, the parameters values aren't emitted to the log. In my case I wanted to log what values were causing Foreign Key violations.

This can be improved by altering NLogCommandInterceptor's LogIfError method like thus

private void LogIfError(DbCommand command, DbCommandInterceptionContext interceptionContext)
{
    if (interceptionContext.Exception != null)
    {
        var commandDumper = new DbCommandDumper(command);
        Log.Warn(Command failed:\r\n{0}", commandDumper.GetLogDump());
        // Exception will get logged further up the stack
    }
}

where the DbCommandDumper class reconstructs the DbCommand into TSQL that can be replayed into a test database.