FSharp.Data | F # Data : Library for Data Access | CSV Processing library

There are two distinct concepts related to mutatation in F#:

• Mutable variables, which are variables that can change value. They are defined using let mutable and you change the value using <- (which is not possible if the variable is not mutable).

• Mutable objects which are just .NET objects that have some mutable state that can be changed by invoking a method on the object. Those are instances of normal C#-style classes.

If you define an immutable variable that is a reference to a mutable object, the object can still be mutated. The fact that the variable is immutable does not prevent that from happening. That is what's happening in your case.

Like there are immutable variables, there are also immutable objects (or values). This includes F# data types like records and discriminated unions. However, the fact whether an object is mutable or not is not tracked in the language - so this is something you do not see in any obvious way.

In well-designed F# code, most of your own objects will be immutable, but most of the .NET objects you are using (to access the functionality provided by .NET) will be mutable - because that's how .NET is designed.

I do not think there is a way to tell JSON provider not to do this, but I agree it would sometimes be useful (in case you wanted to try contributing to the project!)

In the meantime, if you want to iterate over all the values in the array, including nulls, you can use the low-level underlying JsonValue directly. It is less elegant, but lets you do what you need for this one part of JSON processing:

Simply creating a dictionary for lookups solved the issue. I gave up trying to improve further, so posting this as answer.

As per edit replace

Run from command line: dotnet add package microsoft.data.sqlclient

then change Common.DatabaseProviderTypes.MSSQLSERVER to Common.DatabaseProviderTypes.MSSQLSERVER_DYNAMIC

This is about as simple as I could make it, although a longer version might be more readable for you:

The generated type ArrayOrCname should have two properties - Record and Array - which are both optional. If the value is a record, the first one will be Some and the other will be None and vice versa for an array. So, you can handle this using pattern matching. Using your example:

I just created a new console app using .NET Framework 4.8 and FSharp.Data 4.2.3 with no problem.

I noticed that you're redirecting to FSharp.Core 6.0.0. Are you sure you want that?

Anyway, my .fsproj is:

The issue is that the newly created changed invoice does not have the top-level xmlns attributes that are in the original document and define the namespace prefixes. You can fix this by adding those back after creating the new changedInvoice:

You can get access to the original JSON via the .JsonValue property that exists on every object returned by the provider. This property returns type JsonValue, which you can programmatically analyze if you wanted (e.g. calling its Properties() method or some such), and it also has a handly ToString implementation that just returns the serialized JSON: