Adds a new property, FieldName, to ModelBindingContext. The FieldName is
the name of whatever code-element is being bound, regardless of what
model-prefix is in use.
This is needed for cases like the Header model binder. We always want to
use the property/parameter name and we don't care about model prefixes.
- #2836
Part 1: Use existing property values when recursing in `MutableObjectModelBinder`
- remove `ComplexModelDTO` because that indirection made fixing this issue more difficult and doesn't add value
- started with an old closed PR (#2241) which did some of this work
- correct `MutableObjectModelBinderTest` tests that exercised behaviour that can't occur
- the old `dto.Results` dictionary was never incomplete; nor could it contain `null` values
Part 2: Change `MutableObjectModelBinder` to pass complex property values into binding system
- model binding no longer trounces nodes in the model tree that aren't bound
- create model instances less often in `TryUpdateModel` scenarios
- refactor `EnsureModel()` to `GetModel()` and use appropriately
- reorder logic in `SetProperty()` and `AddToProperty()` to avoid copying to / from the same collection
- also cleans up some code duplication
nits:
- clean up `MutableObjectModelBinderTest`
- fix odd line wrappings and indentation
- use `nameof()` more
- use `string.Empty` more
- simplify a couple of `Returns()` expressions
- make assertions in `TryUpdateModelIntegrationTest` more readable
- no need to work through `ModelStateDictionary.Keys`
- also use `Length` instead of `Count()`; test code but we don't need Linq at all in that test class
- use valid `multipart/form-data` content type; include a `boundary`
- correct expectations of `FormCollection` model binder's operation
- restore tests actually skipped for either of the above reasons
- add more tests with `ModelBindingResult.Model==null` and both `IsModelSet` values
#### Remove test references to Won't Fix bug #2473
- restore #2473 tests; update test expectations
- expect `null` composite results whenever binding fails
#### Restore test skipped due to "#2646"
- that issue does not exist; was likely #2466 or similar fixed bug
#### Rename model binding tests that still mention ReturnsFalse or ReturnsTrue
#### Minor src changes
- remove unused variable and unnecessary nesting in `DefaultControllerActionArgumentBinder`
- remove dangling mention of `[DefaultValue]` in `ComplexModelDtoModelBinder`
#### nits:
- remove empty delegates from some `GetOperationBindingContext` calls; `null` fine
- do some `using` cleanup
- combine two test methods in `KeyValuePairModelBinderTest`
- name a few more arguments
Pranav K
Ryan Nowak
Doug Bunting
Harsh Gupta
N. Taylor Mullen