在由SQLite支持的Android ContentProvider中，应如何实现insertOrUpdate语义？

Question

This is in the case where there is a UNIQUE column apart from the _id column.

I can see three options:

1. Leave insert as insert-if-no-conflict, and update as update-if-present (this seems to be the "standard"), and perform all the work on the client to decide how to resolve this.

2. Change insert to insert-or-update-if-present and leave update as update-if-present. Does this break the standard ContentProvider contract?

3. Change update to update-or-insert-if-not-present and leave insert as insert-if-no-conflict. This makes less sense than the second option above to me, so I'll probably not do this - but I suspect it's pretty similar in the end.

Additionally, if I do the first option, is there any advantage in doing

1. query then if count=1, replace, else insert
2. insert, if failed replace
3. replace, if failed insert.

I anticipate more updates than replaces overall, but am mainly concerned with making this maintainable, as I don't expect this to be a performance bottleneck.

Answer 1

My inclination will be to query and then update or insert based on if there is an existing record. You can use the existing ContentProvider methods for this - and it will be quite readable for subsequent developers to understand.

The downside is there's a couple of unnecessary DB hits.

The article talks through how you could modify the ContentProvider to 'implement' insertOrUpdate