JSON: Serializing DataRow into parent object - json

Question

I have a tree structure, created from rows in a DataTable, each DataRow generates one node.
Each node should of course hold the child nodes, but also the source DataRow:
public class TreeNode
{
public List<TreeNode> Items { get; internal set; }
public JToken RowJToken { get; internal set; }
}
(See the code at the end for the reason of RowJToken and not DataRow)
When I serialize the tree structure, I need each TreeNode to be serialized this way (this is dictated by the consuming client):
{
"items": [children],
"columnA": "ValueA",
"columnB": "ValueB",
"columnC": "ValueC"
}
where "[children]" represents the sub-nodes of the node (left out for brevity).
However, the result is instead:
{
"items": [children],
"rowJToken": {
"columnA": "ValueA",
"columnB": "ValueB",
"columnC": "ValueC"
}
}
Question: How can I serialize RowJToken content "on the same level" as the Items array, i.e. not being embedded in the "rowJToken" object?
The set of columns in the DataTable is not known beforehand (but I know the column names don't collide with "items").
Pieces of the code below. Note that the construction of the tree structure itself shouldn't be important in this case.
The reason I store RowJToken instead of DataRow in the TreeNode is that JSON.Net doesn't have a DataRow serializer, but only a DataTable serializer. Thus, I serialize the DataTable into a JArray first, then take the JToken that corresponds to the DataRow and stick that into the TreeNode.
public class TreeNode
{
public JToken RowJToken { get; internal set; }
public List<TreeNode> Items { get; internal set; }
}
...
List<TreeNode> treeNodes = GetTreeNodes(dataTable, childColumnName, parentColumnName);
DefaultContractResolver contractResolver = new DefaultContractResolver
{
NamingStrategy = new CamelCaseNamingStrategy()
};
string json = JsonConvert.SerializeObject(treeNodes, new JsonSerializerSettings
{
ContractResolver = contractResolver,
Formatting = Formatting.Indented
});
...
private List<TreeNode> GetTreeNodes(DataTable dataTable, string childColumnName, string parentColumnName)
{
DataColumn childColumn = dataTable.Columns[childColumnName];
DataColumn parentColumn = dataTable.Columns[parentColumnName];
//
// Use the serializer for DataTable to generate a JSON array, containing each DataRow
//
var jArray = JArray.FromObject(dataTable, JsonSerializer.CreateDefault(new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore }));
//
// The use of "NullObject" is merely to allow NULL values as the key to the dictionary
//
Dictionary<NullObject<string>, List<TreeNode>> hash = new Dictionary<NullObject<string>, List<TreeNode>>();
var rowIndex = 0;
foreach (DataRow r in dataTable.Rows)
{
string childId = r.Field<string>(childColumn);
string parentId = r.Field<string>(parentColumn);
if (!hash.TryGetValue(childId, out List<TreeNode> childIdTreeNodes))
{
childIdTreeNodes = new List<TreeNode>();
hash.Add(childId, childIdTreeNodes);
}
if (!hash.TryGetValue(parentId, out List<TreeNode> parentIdTreeNodes))
{
parentIdTreeNodes = new List<TreeNode>();
hash.Add(parentId, parentIdTreeNodes);
}
//
// Put the JToken which corresponds to this DataRow in the TreeNode
//
var rowJToken = jArray[rowIndex++];
parentIdTreeNodes.Add(new TreeNode()
{
Items = childIdTreeNodes,
RowJToken = rowJToken
});
}
//
// Return the root node(s), i.e. the nodes with NULL as parent ID
//
return hash[null];
}

Answer 1

You can get the output you want with a few simple changes.
In your TreeNode class, change the type of the RowJToken from JToken to JObject. (You might also want to change the property name to RowJObject as well, to be consistent, but that is not strictly necessary.)
public JObject RowJToken { get; internal set; }
Decorate the RowJToken property with a [JsonExtensionData] attribute.
[JsonExtensionData]
public JObject RowJToken { get; internal set; }
In your GetTreeNodes method, cast the JToken that is retrieved from the jArray to a JObject.
var rowJToken = (JObject)jArray[rowIndex++];
And that's it. When you serialize the treeNodes list, the RowJToken properties for each TreeNode will be on the same level as its respective Items array.
Proof of concept: https://dotnetfiddle.net/LEaeXo