I am not sure I completely understand the problem. Are you referring to the cilent-side or server-side datasource object?
What the chart uses is a simple list of JSON objects (i.e. no deep nesting of objects inside a field of the original object) on the client and thus a simple datatable on the client. The DataFieldY property points to a column name and the code-behind takes the value stored in that column, so it has to be either a string for labels, or a number for values, or boolean for ExplodeField in a PieChart.
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