Question

Given the following code (which is mostly irrelevant except for the last two lines), what would your method be to get the value of the identity field for the new record that was just created? Would you make a second call to the database to retrieve it based on the primary key of the object (which could be problematic if there’s not one), or based on the last inserted record (which could be problematic with multithreaded apps) or is there maybe a more clever way to get the new value back at the same time you are making the insert?

Seems like there should be a way to get an Identity back based on the insert operation that was just made rather than having to query for it based on other means.

public void Insert(O obj)
{
    var sqlCmd = new SqlCommand() { Connection = con.Conn };
    var sqlParams = new SqlParameters(sqlCmd.Parameters, obj);
    var props = obj.Properties.Where(o => !o.IsIdentity);

    InsertQuery qry = new InsertQuery(this.TableAlias);
    qry.FieldValuePairs = props.Select(o => new SqlValuePair(o.Alias, sqlParams.Add(o))).ToList();

    sqlCmd.CommandText = qry.ToString();
    sqlCmd.ExecuteNonQuery();
}

EDIT: While this question isn’t a duplicate in the strictest manner, it’s almost identical to this one which has some really good answers: Best way to get identity of inserted row?

Answer 1

It strongly depends on your database server. For example for Microsoft SQL Server you can get the value of the @@IDENTITY variable, that contains the last identity value assigned.

To prevent race conditions you must keep the insert query and the variable read inside a transaction.

Another solution could be to create a stored procedure for every type of insert you have to do and make it return the identity value and accept the insert arguments.

Otherwise, inside a transaction you can implement whatever ID assignment logic you want and be preserved from concurrency problems.