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Refactor database schema constants

username-removed-25042 requested to merge pserwylo/fdroidclient:fix-511--database-constants into master

Note: When this is merged I'll rebase !347 (merged) and remove its WIP.

Summary

In order to do the database changes required for #511 (closed), I've found that it is difficult due to my inclination to switch between referring to database columns by either a Java constant such as AppProvider.DataColumns.NAME and string literals such as "name". All string literals should be migrated to constants, and that will happen in my next MR. In order to prepare for this, I've gathered together the constants into one common place: org.fdroid.fdroid.data.Schema. This is going to be the authoritative place for the schema to be stored going forward, and will help when reasoning about the database structure.

Although it seems large, this change is a fairly straightforward find/replace job. It also passes all tests for which there is good test coverage in the content providers.

Changes

Create Schema interface to make it simpler to replace string literals with constants.

Right now, table names are in DBHelper.TABLE_* constants, and each tables fields are in *Provider.DataColumns.* constants. This brings them all into a predictable location. In addition, it makes it easier to statically import Schema so that instead of, e.g.,

  • AppProvider.DataColumns.PACKAGE_NAME

We can choose one of the following, based on our current context:

  • Schema.AppTable.Cols.PACKAGE_NAME
  • AppTable.Cols.PACKAGE_NAME
  • Cols.PACKAGE_NAME

In the worst case, it isa couple of chars shorter than now. In the best case, if we are writing a class that primarily deals with Apps (e.g. App.java or AppProvider.java) then we get a big win with just Cols.PACKAGE_NAME.

Having these things slightly shorter may seem like it is pointless, but the length of each constant probably contributed to my lack of willingness to use constants instead of string literals when constructing queries.

In the future, this should be moved towards something more akin to:

http://openhms.sourceforge.net/sqlbuilder/

and I hope that extracting all the schema stuff into one interface may help that.

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