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Converting DataTables to JSON

When I started creating Web Services, I was using ADO.NET DataSets to retrieve data and then sending that data to my consumers using XML. Those Web Services are still there, but my consumers now want JSON.

The good news is that I don't have to rewrite my code to return the data in the right format. While I could switch to using SQL Server's new ability to convert query results into JSON, the existing code has that whole "working" feature that people like so much -- I have no desire to replace it.

The people who created NewtonSoft.JSON saw this problem coming and provided a solution for converting DataSet tables into JSON. First, you need to extract the DataTable holding your rows from your DataSet:

Dim dt As DataTable
dt = MyDataSet.Tables("Customers")

Then create a JsonServializer:

Dim js As JsonSerializer
js = JsonSerializer.CreateDefault

At this point you could set properties on the JsonSerializer to control how your JSON will be generated.

Next, pass your DataTable and Serializer to the FromObject method on NewtonSoft's JArray class. The FromObject method will convert all the rows in your DataTable into an array of JToken objects, held in a JArray object:

Dim rows As JArray
rows = JArray.FromObject(dt, js)

Now you can send the whole collection to the consumer:

Return rows.ToString()

Alternatively, you use LINQ to pull out the rows you want. This gets the first row, for example, and sends it to the consumer:

Dim row As JToken
row = rows.FirstOrDefault
Return row.ToString

Posted by Peter Vogel on 05/29/2018 at 11:03 AM


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