Flattening out a JToken

问题

Suppose I have the following JToken:

@"{
    ""data"": [
        {
            ""company"": {
                ""ID"": ""12345"",
                ""location"": ""Some Location""
            },
            ""name"": ""Some Name""
        }
    ]
}";

I want to pass this token into a FlattenToken function that outputs this JToken:

@"{
    ""data"": [
        {
            ""company_ID"": ""12345"",
            ""company_location"": ""Some Location"",
            ""name"": ""Some Name""
        }
]}"

The reason for doing this is so that I can then take the flattened JToken and deserialize it into a DataTable.

I'm getting lost in a jumble of JObjects, JTokens, JProperties, and other JMadness, though. I saw the answer on this post, which was helpful, but I'm still not getting it right.

Here's what I have so far:

public static JToken FlattenToken(JToken token)
{
    foreach (JToken topLevelItem in token["data"].Children())
    {
        foreach (JToken field in topLevelItem.Value<JToken>())
        {
            foreach (JProperty property in field.Value<JObject>().Properties())
            {
                field.AddAfterSelf(JObject.Parse(@"{""" + property.Name + "_" + property.Value));
            }

            field.Remove();
        }
    }

    return token;
}

The first iteration through the outer foreach loop, topLevelItem =

{
    "company": {
        "ID": "12345"
    },
    "name": "Some Name"
}

And the first iteration through the second foreach loop, field =

"company": {
    "ID": "12345"
}

Looking good so far. But when I hit the innermost foreach loop, I get an exception on the foreach line: "Cannot cast Newtonsoft.Json.Linq.JProperty to Newtonsoft.Json.Linq.JToken."

Not sure what's going on there. I was under the impression that the field.Value call was going to produce a JToken and try to cast it to a JProperty. So where is a JProperty trying to be casted to a JToken, as the error suggests?

Also, this feels like a pretty gross way of flattening out a JToken. Is there a better way?

回答1:

The hierarchy of objects in Json.NET can be rather deep. A rough guide can be found in this answer.

To solve your problem, you first need an extension method to take the properties of a JObject and return then in a collection with a name prefix:

public static class JsonExtensions
{
    public static IEnumerable<KeyValuePair<string, JToken>> FlattenFields(this JObject obj, string prefix)
    {
        foreach (var field in obj)
        {
            string fieldName = prefix + "_" + field.Key;
            var fieldValue = field.Value;
            yield return new KeyValuePair<string, JToken>(fieldName, fieldValue);
        }
    }
}

Next, you need some recursive tools to iterate through a Json.NET hierarchy and rewrite the collection of properties of selected JObject's:

public static class JsonExtensions
{
    public static IEnumerable<T> Yield<T>(this T item)
    {
        yield return item;
    }

    public static JToken EditFields(this JToken token, Func<KeyValuePair<string, JToken>, IEnumerable<KeyValuePair<string, JToken>>> editor)
    {
        if (token == null)
            return null;
        switch (token.Type)
        {
            case JTokenType.Array:
                return EditFields((JArray)token, editor);
            case JTokenType.Object:
                return EditFields((JObject)token, editor);
            default:
                return token;
        }
    }

    static JToken EditFields(JArray array, Func<KeyValuePair<string, JToken>, IEnumerable<KeyValuePair<string, JToken>>> editor)
    {
        JArray newArray = null;
        foreach (var element in array)
        {
            var newElement = EditFields(element, editor);
            if (newElement != null)
            {
                if (newArray == null)
                    newArray = new JArray();
                newArray.Add(newElement);
            }
        }
        return newArray;
    }

    static JToken EditFields(JObject obj, Func<KeyValuePair<string, JToken>, IEnumerable<KeyValuePair<string, JToken>>> editor)
    {
        JObject newObj = null;

        foreach (var field in obj)
        {
            foreach (var newField in editor(field))
            {
                if (newObj == null)
                    newObj = new JObject();
                newObj[newField.Key] = newField.Value.EditFields(editor);
            }
        }

        return newObj;
    }
}

Finally, put these together to create a method that promotes properties of a named JObject property to their parent JObject, prepending the property name plus an underscore:

public static class JsonExtensions
{
    public static JToken PromoteNamedPropertiesToParents(this JToken token, string propertyName)
    {
        return token.EditFields(pair =>
        {
            if (pair.Key == propertyName && pair.Value is JObject)
            {
                return ((JObject)pair.Value).FlattenFields(pair.Key);
            }
            return pair.Yield();
        });
    }
}

And then, to test:

public static class TestFlatten
{
    public static void Test()
    {
        string jsonString = @"{
            ""data"": [
                {
                    ""company"": {
                        ""ID"": ""12345"",
                        ""location"": ""Some Location""
                    },
                    ""name"": ""Some Name""
                }
            ]
        }";
        JObject obj = JObject.Parse(jsonString);
        var newObj = (JObject)obj.PromoteNamedPropertiesToParents("company");
        Debug.WriteLine(newObj);
    }
}

And the output is:

{
  "data": [
    {
      "company_ID": "12345",
      "company_location": "Some Location",
      "name": "Some Name"
    }
  ]
}

Which is what you want. Please note that this code creates a new JObject hierarchy rather than modifying the original hierarchy.

来源：https://stackoverflow.com/questions/27713897/flattening-out-a-jtoken