Using a GridView to make calculations and avoid Database changes by merging DataTables and using PrimaryKey.

Merging DataTables named dt and dt2.

Before I show the diffences, here are the contents of dt (Figure 1) and dt2 (Figure 2):

Symbol	Name	Exchange
FRE	Freddie Mac	NYSE
FRE/PB	Freddie Mac	NYSE
FRE/PF	Freddie Mac	NYSE
FRE/PG	Freddie Mac	NYSE
FRE/PH	Freddie Mac	NYSE

Figure 1. dt

Symbol	EPS Growth	Lower Price Target	Lower % Target	Upper Price Target	Upper % Target
FRE	FRE	FRE	FRE	FRE	FRE
FRE/PB	FRE/PB	FRE/PB	FRE/PB	FRE/PB	FRE/PB
FRE/PF	FRE/PF	FRE/PF	FRE/PF	FRE/PF	FRE/PF
FRE/PG	FRE/PG	FRE/PG	FRE/PG	FRE/PG	FRE/PG
FRE/PH	FRE/PH	FRE/PH	FRE/PH	FRE/PH	FRE/PH

Figure 2. dt2

In my project I want to use a GridView and append calculated data without changing the database.
My solution is to read the GridView into a DataTable, dt. Then, I make calculations from a PrimaryKey of dt and use the same PrimaryKey for dt2 while adding actual calculations (EPS Growth, Lower Price Target, ... in production version). The final step is to Merge the datatables with dt.Merge(dt2). The result is shown in Figure 3.

Symbol	Name	Exchange	EPS Growth	Lower Price Target	Lower % Target	Upper Price Target	Upper % Target
FRE	Freddie Mac	NYSE	FRE	FRE	FRE	FRE	FRE
FRE/PB	Freddie Mac	NYSE	FRE/PB	FRE/PB	FRE/PB	FRE/PB	FRE/PB
FRE/PF	Freddie Mac	NYSE	FRE/PF	FRE/PF	FRE/PF	FRE/PF	FRE/PF
FRE/PG	Freddie Mac	NYSE	FRE/PG	FRE/PG	FRE/PG	FRE/PG	FRE/PG
FRE/PH	Freddie Mac	NYSE	FRE/PH	FRE/PH	FRE/PH	FRE/PH	FRE/PH

Figure 3.

If you simply Merge with dt.Merge(dt2), you would get the same result as long as the PrimaryKey is set in dt. However, without setting the PrimaryKey you get the result in Figure 4.

Symbol	Name	Exchange	EPS Growth	Lower Price Target	Lower % Target	Upper Price Target	Upper % Target
FRE	Freddie Mac	NYSE
FRE/PB	Freddie Mac	NYSE
FRE/PF	Freddie Mac	NYSE
FRE/PG	Freddie Mac	NYSE
FRE/PH	Freddie Mac	NYSE
FRE			FRE	FRE	FRE	FRE	FRE
FRE/PB			FRE/PB	FRE/PB	FRE/PB	FRE/PB	FRE/PB
FRE/PF			FRE/PF	FRE/PF	FRE/PF	FRE/PF	FRE/PF
FRE/PG			FRE/PG	FRE/PG	FRE/PG	FRE/PG	FRE/PG
FRE/PH			FRE/PH	FRE/PH	FRE/PH	FRE/PH	FRE/PH

Figure 4.

In my implementation I use:
dt.Merge(dt2, false, MissingSchemaAction.Ignore);
This will avoid preserving changes and ignore taking action when there is a missing schema.