Mathematica: GOTCHA: Setting the value of a property of an Entity using EntityValue[e,"property"] where 'e' is an Entity does NOT work with a relational database backed EntityStore, which undermines half the point of a relational database bridge!

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Note kind
GOTCHA
ISSUE
LIMITATION
Policy level
INFORMATIVE
Mathematica keywords
Entity
EntityStore
EntityProperty
EntityValue
ExternalEvaluate
RelationalDatabase
DatabaseReference
Keywords
If you have a purely expression-based EntityStore in a Notebook, the following sets the value of a "property" for an Entity 'e': 
EntityValue[e, "property"] = value

But not so for relational database backed EntityStore!:

Set::write: Tag EntityValue in EntityValue[...,.. is Protected.
In other words, of CRUD = (C)reate-(R)ead-(U)pdate-(D)elete you only get (R)ead (query), which undermines half the point of a database bridge!

You have to use raw SQL with ExternalEvaluate. Not cool.

Visit also:
Mathematica: GOTCHA/LIMITATION: RelationalDatabase and DatabaseReference are NOT supported in the Wolfram Cloud for "public" accounts, not even for Premium Plan (Commercial)! It is only optionally offered on the Wolfram Enterprise Private Cloud (EPC).
Mathematica: GOTCHA/LIMITATION: Changing the value of an Entity in an expression-based EntityStore loaded from a CloudObject does not update the CloudObject. You have to push the EntityStore back to the CloudObject. It is not like a "live" connection.
Mathematica: GOTCHA: If you pull an EntityStore from a CloudObject with PersistentSymbol it caches and will not update if invoked again even if the CloudObject for the EntityStore has changed. Use instead CloudGet.
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