View source for Training:Import data from other SQL servers

{{Edited|July|12|2025}}
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MDriven Server has been extended with functionality to import data from other SQL-based systems.

The MDriven Server is designed to take care of the repetitive common tasks that always seem to come back and haunt system developers. MDriven Server takes a strictly model-driven approach to help you with the work.

Earlier, I described how to export files: [[Training:Exporting files from MDriven Server|Exporting files from MDriven Server#Producing export files from MDriven Server]]

and here is a link to where I explain more about the concept of periodic actions: [[Training:MDrivenServer periodic server-side actions|MDrivenServer periodic server-side actions]]

What is new today is the ability to read from an external SQL server and import that data – strictly by using MDriven techniques - with zero need for external programs.

Let me show you.

Suppose I have this model and I want Class1 to be reference data from an external database:

[[File:ServerSide Actions Importing Data 01.png|frameless|257x257px]]

I declare a ViewModel that looks like this:

[[File:ServerSide Actions Importing Data 02.png|frameless|469x469px]]

It defines 4 columns with data and 2 actions:

1=<u>'''ViewModel / new [[Documentation:Nestings|Nesting]]'''</u> – the name of yet another ViewModel that will act as an importer of the SQL result set, this can, in recent versions, be replaced with '''Nesting''' and then you are expected to have a connected nesting with that name in the ViewModel that has the Import action. This '''Nesting''' is then defining the columns to import.
[[File:2019-02-05 15h42 14.png|none|thumb|This shows how the Nesting column ties to Nesting inside the same ViewModel. ]]

2='''<u>Connectionstring</u>'''- the external database (''<u>Update 2018-10-18</u>: you can now use 'connectionstringodbc' and the logic will use ODBC connection instead of sqlserver.'')

3=<u>'''Query'''</u> – the SQL query (remember that you can build it with data from the rest of your model).

4=<u>'''Key'''</u> – if we want the import to be able to update Class1, we need to explain what the key is in the class. The value of the key should be a string with the value of the name of the attribute we want to use as a key in the class. This attribute must also be the result of the first column on the import nesting.

And the actions:

'''SQLImport''' – using this name will trigger the import function in MDriven Server.

'''Finished''' – this is a generic action that executes the expression - in this case setting Class2.Attribute1 to ‘Done’.

So the returned SQL data looks like this:

[[File:ServerSide Actions Importing Data 03.png|frameless|323x323px]]

And the ViewModel that is going to act as the import template – called “TheImporter” in the example above - looks like this:

[[File:ServerSide Actions Importing Data 04.png|frameless]]

I now declare the ServerSide job in MDriven Server:

[[File:ServerSide Actions Importing Data 05.png|frameless|422x422px]]

Now the MDriven Server will check every 20 seconds if the expression: 
 Class2.allinstances- >select(attribute1=’todo’)
returns any rows. If it does, it fetches at most 2 of these and executes all the actions found in TheServerSideJob.

In MDriven Designer, I can create a Class2 with the debugger and save it:

[[File:ServerSide Actions Importing Data 06.png|frameless|324x324px]]

And then I check the MDriven Server log: [[File:ServerSide Actions Importing Data 07.png|frameless|493x493px]]

I check my Class2:                              [[File:ServerSide Actions Importing Data 08.png|frameless|448x448px]]

Attribute1 is now ‘Done’ – so the serverside job relaxes and will not find anything more to do for now.

=== Rewriting From Old Style 2 ViewModels to New Style 1 ViewModel with Nesting ===
The old style was to have a ViewModel column pointing out the description of the import row. The new more compact style is to instead refer to a Nesting within the main ViewModel doing the import.

Example of the new style:
[[File:2019-05-15 10h38 46.png|none|thumb|610x610px]]
Example of the old style:
[[File:2019-05-15 10h41 20.png|none|thumb|980x980px]]Make sure the columns in the import are not left as read-only since they are created that way by default. If they are read-only, they will not receive any values:
[[File:2020-04-21 11h47 05.png|none|thumb|939x939px]]'''<span style="color: #1a50ad">The MDriven Book</span>''' - '''Next Chapter:''' [[Exporting files from MDriven Server]]
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