fix(Model): retrieve correct associated target name

[ruiguoamz]

Issue #, if available:
Alternative of fixing: #512

Description of changes:
An alternative for this PR which was reverted: #885

Moved func modelName(forField: fieldName) to AmplifyPluginsCore so that both API and DataStore can reuse the logic.

• API: While the getGraphQLFilter(_ modelSchema: ModelSchema) is returned with the correct fieldName
• DataStore: At the time sql is translated from QueryPredicate, the correct columnName for belongsTo and hasOne field can be retrieved from modelSchema.association. In this case, CLI change is not required.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #965 (1795c2b) into main (9e32cf7) will increase coverage by 0.02%.
The diff coverage is 68.42%.

@@            Coverage Diff             @@
##             main     #965      +/-   ##
==========================================
+ Coverage   55.54%   55.57%   +0.02%     
==========================================
  Files         634      634              
  Lines       18373    18401      +28     
==========================================
+ Hits        10206    10227      +21     
- Misses       8167     8174       +7     

Flag	Coverage Δ
API_plugin_unit_test	48.09% <ø> (ø)
AWSPluginsCore	71.88% <69.04%> (-0.53%)	⬇️
Amplify	45.87% <0.00%> (+0.12%)	⬆️
Analytics_plugin_unit_test	73.41% <ø> (ø)
Auth_plugin_unit_test	73.60% <ø> (ø)
DataStore_plugin_unit_test	71.01% <83.33%> (-0.03%)	⬇️
Predictions_plugin_unit_test	33.48% <ø> (ø)
Storage_plugin_unit_test	57.72% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ies/DataStore/Model/Collection/List+LazyLoad.swift	0.00% <0.00%> (ø)
...aphQLRequest/GraphQLRequest+AnyModelWithSync.swift	81.31% <0.00%> (ø)
...re/Model/GraphQLRequest/GraphQLRequest+Model.swift	70.42% <0.00%> (ø)
...yPlugin/Storage/SQLite/QueryPredicate+SQLite.swift	100.00% <ø> (ø)
...goryPlugin/Storage/SQLite/ModelSchema+SQLite.swift	97.05% <50.00%> (-2.95%)	⬇️
...insCore/Model/Support/QueryPredicate+GraphQL.swift	73.80% <76.31%> (-6.20%)	⬇️
...Plugin/Storage/SQLite/SQLStatement+Condition.swift	98.00% <90.00%> (-2.00%)	⬇️
...CategoryPlugin/Operation/AWSGraphQLOperation.swift	60.75% <0.00%> (-2.54%)	⬇️
.../DataStore/Model/Internal/Schema/ModelSchema.swift	88.23% <0.00%> (+2.94%)	⬆️
... and 3 more

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[lawmicha]

looks like there's an extension on ModelField+Schema that already generates the columnName
https://github.com/aws-amplify/amplify-ios/blob/main/AmplifyPlugins/DataStore/AWSDataStoreCategoryPlugin/Storage/SQLite/ModelSchema+SQLite.swift#L42-L73

[lawmicha]

no action needed just a thought exercise.. If developers use QueryPredicateConstant.all then it will fail. Is there a way for developers to get into this state?

1. Calling API directly with a predicate .all and app will crash. This is probably okay since it is not supported to use .all
2. Is there a scenario which is calling into DataStore, and then it gets synced to the API and fail here? If so, this may be a bigger concern, what should API do when they see a predicate that is ".all"?

Secondly, precondionFailure affects live apps as well. In one of my latest PR's, I've started using assert(false, "message") instead so that it crashes only during debug builds, and not on release builds

[lawmicha]

add doc comment for the public API, i see up above

/// Extension to translate a `QueryPredicate` into a GraphQL query variables object

perhaps this information can be on top of the method as well. just a suggestion since i recall the discussion regarding adding doc comment and warning, etc. something like

/// Retrieve the GraphQL representation of the `QueryPredicate`. This translates the `QueryPredicate` into a 
/// JSON object, useful for passing as the "filter" or "condition" input of the GraphQL variables. For example
/// <Query Predicate example to JSON string>
///
/// - Warning: Although this has `public` access, it is intended for internal use and should not be used directly
///   by host applications. The behavior of this may change without warning.