how to parse an Enum Structure in vb.net

[Herfried K. Wagner [MVP]]

I have an Enum Structure

Public Enum MyEnum
EnumVal1=0
EnumVal2=1
EnumVal2=2

end enum

I save in an access database this enum value as an integer (0=EnumVal1,
1=EnumVal2, 2=EnumVal)

\\\
Dim e As MyEnum = CType(v, MyEnum)
///

 

[giannik]

I have an Enum Structure

Public Enum MyEnum
EnumVal1=0
EnumVal2=1
EnumVal2=2

end enum

I save in an access database this enum value as an integer (0=EnumVal1,
1=EnumVal2, 2=EnumVal)


When retreving this enum from the database how do I ensure that the correct
value is passed to my object

For instance


MyObject.MyEnum=1 .
Does this populate the property with MyObject.MyEnum= EnumVal2
giannik

 

[Patrice]

You have nothing special to do. See EnumVal2 has being just a symbolic name
for the value 1 (similarly to a constant).

So if MyObject.MyEnum=1, MyObject.MyEnum=MyEnum.EnumVal2 because
MyEnum.EnumVal2 is also 1.

 

[giannik]

ok. Thank you very much

You have nothing special to do. See EnumVal2 has being just a symbolic
name for the value 1 (similarly to a constant).

So if MyObject.MyEnum=1, MyObject.MyEnum=MyEnum.EnumVal2 because
MyEnum.EnumVal2 is also 1.

 

[Phill W.]

I have an Enum

Public Enum MyEnum
EnumVal1=0
EnumVal2=1
EnumVal2=2
end enum

I save in an access database this enum value as an integer (0=EnumVal1,
1=EnumVal2, 2=EnumVal)

Save the Enum /names/ not their numeric values.
OK, you only have three here, but what if you had a long list of these
and then, Lord forbid, you added another one "in the middle"? Much of
your existing data (in Access) would be wrong.

When retreving this enum from the database how do I ensure that the correct
value is passed to my object

When reading the property back, parse the string value (from Access)
back into the Enum Type, as in

MyObject.MyEnum = CType( dr.Item( "EV" ), MyEnum )

By way of a rather silly example:

Class MyClass
Enum Month
January = 1
February
March
. . .

dr.Item( "Month" ) = Month.December.ToString() ' actually "December"

Now, just for the sake of argument, let's create a new month, called
Filibuster, between February and March.

Class MyClass
Enum Month
January = 1
February
Filibuster
March
. . .

Oh No! I hear you cry. You'll have to bulk update all the records in
Access to increment their month numbers!
Nope. Holding the Enum /names/ means you don't have to. Assuming you
already have a row in there for December:

? dr.Item( "Month" ).GetType().ToString()
[System.]String
? dr.Item( "Month" ).ToString()
"December"
? CType( dr.Item( "Month" ), Month ).GetType().ToString()
[MyClass.]Month
? CType( dr.Item( "Month" ), Month )
December

So far, so good, but here's the clincher ...

? CInt( dr.Item( "Month" ), Month )
13

.... even if it was 12 when you saved that record into Access!

HTH,
Phill W.

 

[Guest]

It seems a waste to use strings as opposed to integers in a database for
ENUMS. You can just as easily assign numbers to each enum value, i.e.,

Enum Month
January = 10
February = 20
March = 30
. . .

In the new enum;
Enum Month
January = 10
February =20
Filibuster = 25
March =30
. . .

--
Dennis in Houston

I have an Enum

Public Enum MyEnum
EnumVal1=0
EnumVal2=1
EnumVal2=2
end enum

I save in an access database this enum value as an integer (0=EnumVal1,
1=EnumVal2, 2=EnumVal)

Save the Enum /names/ not their numeric values.
OK, you only have three here, but what if you had a long list of these
and then, Lord forbid, you added another one "in the middle"? Much of
your existing data (in Access) would be wrong.

When retreving this enum from the database how do I ensure that the correct
value is passed to my object

When reading the property back, parse the string value (from Access)
back into the Enum Type, as in

MyObject.MyEnum = CType( dr.Item( "EV" ), MyEnum )

By way of a rather silly example:

Class MyClass
Enum Month
January = 1
February
March
. . .

dr.Item( "Month" ) = Month.December.ToString() ' actually "December"

Now, just for the sake of argument, let's create a new month, called
Filibuster, between February and March.

Class MyClass
Enum Month
January = 1
February
Filibuster
March
. . .

Oh No! I hear you cry. You'll have to bulk update all the records in
Access to increment their month numbers!
Nope. Holding the Enum /names/ means you don't have to. Assuming you
already have a row in there for December:

? dr.Item( "Month" ).GetType().ToString()
[System.]String
? dr.Item( "Month" ).ToString()
"December"
? CType( dr.Item( "Month" ), Month ).GetType().ToString()
[MyClass.]Month
? CType( dr.Item( "Month" ), Month )
December

So far, so good, but here's the clincher ...

? CInt( dr.Item( "Month" ), Month )
13

.... even if it was 12 when you saved that record into Access!

HTH,
Phill W.

 

[Guest]

Storing the integer value rather than the name does perform better.
Storing the names is something that should be considered in some cases,
though.

In some cases the names correspond naturally to a number that won't
change, for an example the months that are numbered from 1 through 12.
Then there is no reason to store the name instead of the number.

In other cases the names have no natural numbering at all, then it might
be better to store the names. The numbers are only used internally by
the application, and the data in the database is meningful without a
translation table.