Metadata should be read/write capable independently

[danthorpe]

Currently I can write my Item without writing its Metadata by setting the metadata property to nil, there's no way to conversely write the Metadata without also writing the Item.

There also doesn't appear to be a way to read either one without reading them both. This may seem odd, given that my original request was that I wanted to be able to read them together, which I now can, but I'd still like to be able to read them separately if needed.

Neither of these are really that big of a deal and may just be me prematurely optimizing, but as I'm refactoring my code to use the new API these have come up and I thought I'd run them by you.

[danthorpe]

Yeah, that's all a fair point. The functional API got scaled back in a few places, including the readMetadataAtIndex: function. Will add it back.

[danthorpe]

So, I'll add readMetadata APIs, but don't probably will not add the API to read the object without the metadata. Unless that's an argument with default on the primary readAtIndex and readAtKey.

[danthorpe]

Also, just to clarify, YapDatabase doesn't support writing the metadata without writing the object. From the docs, it says if you pass nil for the object, it will remove the object from the database. So, I will not add a writeMetadata API.

Also, it is not possible to have a readMetadataByKey API, as the collection cannot be inferred from the MetadataType alone. While it is possible to write the function, using the object type, and returning the nested Object.MetadataType. However, when it comes to calling such a method, it will not work as I guess the compiler cannot infer the parent type from nested types. For example, given a function (which will compile)

func readMetadataByKey<
    PersistableWithObjectMetadata where
    PersistableWithObjectMetadata: Persistable,
    PersistableWithObjectMetadata.MetadataType: NSCoding>(key: String) -> PersistableWithObjectMetadata.MetadataType? {
        return readMetadataAtIndex(PersistableWithObjectMetadata.indexWithKey(key))
}

trying to use it...

let metadata: MyObject.MetadataType? = readMetadataByKey(aKey)

will not compile. So, instead, you'd have to call readMetadataAtIndex directly.

let metadata: MyObject.MetadataType? = readMetadataAtIndex(MyObject.indexWithKey(aKey))

[codecov-io]

Current coverage is 82.61%

Merging #56 into development will increase coverage by +0.98% as of bffd021

@@            development     #56   diff @@
===========================================
  Files                18      22     +4
  Stmts              1165    1231    +66
  Branches              0       0       
  Methods                               
===========================================
+ Hit                 951    1017    +66
  Partial               0       0       
  Missed              214     214       

Review entire Coverage Diff as of bffd021

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[aranasaurus]

Yap database doesn't have a writeMetadata.. but does have a replaceMetadata... method, which makes sense since you can't write a metadata by itself unless it already exists attached to an object.

Makes sense to have to use the full index to get the metadata separately as well, thanks for that!

[danthorpe]

@aranasaurus well, may add a set of replace functions at some point in the future.