Creating AutoIncrement Columns
ADO.NET supports columns that increment automatically to ensure that
values are unique when new rows are added to the table. These
properties are AutoIncrement
,
AutoIncrementSeed
, and
AutoIncrementStep
. The following code demonstrates
creation of an
AutoIncrement
column:
DataColumn col = new DataColumn("Id", typeof(System.Int32)); col.AutoIncrement = true; col.AutoIncrementSeed = -1; col.AutoIncrementStep = -1;
The code uses seed and step values of -1. This causes the values for
the added rows to start at -1, with subsequent values of -2, -3, and
so on, which ensures that the automatically generated values will not
already exist in a data source with an
AutoIncrement
key containing only positive values.
When the data is updated back to the data source, the added records
are correctly identified as new records, inserted into the data
source, and at that point the AutoIncrement
value
can be returned from the data source and update the negative value in
the DataSet
. Returning the
AutoIncrement
values generated from the data
source is discussed in more detail in Chapter 15.
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