How should I store this information?

I have a PrivilegeGroup table, a Privileges table and a link table because the PrivilegeGroup table and the Privileges table is a many to many relationship. I am thinking about load all contents of PrivilegeGroup table and Privilege table into memory from data开发者_如何学Pythonbase at beginning when application started.

I want to save them in a form easily to look up. Usually we will look up the PrivilegeCode via GroupId.

Which structure is good for this purpose? array of list? dictionary?

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It sounds like you want to be able to look up PrivelegeCode by the GroupId and don't need any other data? If that is the case then you could use a Dictionary<GroupIdDataType, PrivelegeCodeDataType> which should make the lookups easy.

As for loading them all at once on starting the application, I guess it just depends on if changes to this data while the application is running should have any effect on the program without having to restart it.

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How about

Dictionary<GroupIdType, HashSet<PrivilegeCodeType>>

This way you can quickly get the HashSet of privileges by GroupId, and do a quick test against the HashSet to check if the privilege exists.

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I'll suggest you to keep the data in the instance of DataTable class.