[C#] Exception thrown when creating schema with multiple columns with the same name

[DanTm99]

Describe the bug, including details regarding any error messages, version, and platform.

When creating a Schema Schema.cs, if the list of Fields contains fields that share the same name, an exception is thrown when constructing the fields dictionary.

The use of a dictionary disallows multiple fields that have the same name, even though it should be allowed.

Component(s)

C#

[DanTm99]

This exception is thrown when constructing the _fieldsDictionary, because the keys for it are the field names and a dictionary cannot have multiple entries with the same key.

This is publicly exposed as IReadOnlyDictionary<string, Field> Fields, and avoiding this exception would require either skipping fields with duplicate names when constructing it (making the dictionary an inaccurate representation of the fields), or by replacing the IReadOnlyDictionary<string, Field> with another type (e.g. ILookup<string, Field> or IReadOnlyList<Field>) which would be a breaking change for anyone using Fields directly.

@westonpace @eerhardt thoughts?

[westonpace]

Yes, that is my understanding. I think maintaining backwards compatibility (by skipping fields) is ok, maybe even preferred, if we can mark the API as deprecated. However, we would need to ensure we don't break anything internally. For example, if we read from an IPC file into a table, slice the table, and then write a new IPC file, it should still have all the fields. This would mean we'd have to update internal APIs to avoid using this deprecated field (though marking it as deprecated would probably lead us to do that anyways).