Possible to search case-insensitive with JSONPath?

Question

Using the SelectToken method of JSON.NET to select a token with JSONPath, I found no way to specifiy that the search should be case-insensitive.

E.g.

jso         


        

Answer 1

This is not implemented in Json.NET as of version 8.0.2.

JSONPath property name matching is done with two classes: FieldFilter for simple name matches, and ScanFilter for recursive searches. FieldFilter has the following code, where o is a JObject:

JToken v = o[Name];
if (v != null)
{
    yield return v;
}

Internally JObject uses a JPropertyKeyedCollection to hold its properties, which in turn uses the following comparer for property name lookups:

private static readonly IEqualityComparer Comparer = StringComparer.Ordinal;

It is thus case-sensitive. Similarly, ScanFilter has:

JProperty e = value as JProperty;
if (e != null)
{
    if (e.Name == Name)
    {
        yield return e.Value;
    }
}

Which is also case sensitive.

There's no mention of case-insensitive matching in the JSONPath standard so I think what you want simply isn't available out of the box.

As a workaround, you could add your own extension methods for this:

public static class JsonExtensions
{
    public static IEnumerable CaseSelectPropertyValues(this JToken token, string name)
    {
        var obj = token as JObject;
        if (obj == null)
            yield break;
        foreach (var property in obj.Properties())
        {
            if (name == null)
                yield return property.Value;
            else if (string.Equals(property.Name, name, StringComparison.OrdinalIgnoreCase))
                yield return property.Value;
        }
    }

    public static IEnumerable CaseSelectPropertyValues(this IEnumerable tokens, string name)
    {
        if (tokens == null)
            throw new ArgumentNullException();
        return tokens.SelectMany(t => t.CaseSelectPropertyValues(name));
    }
}

And then chain them together with standard SelectTokens calls, for instance:

var root = new { Array = new object[] { new { maxAppVersion = "1" }, new { MaxAppVersion = "2" } } };

var json = JToken.FromObject(root);

var tokens = json.SelectTokens("Array[*]").CaseSelectPropertyValues("maxappversion").ToList();
if (tokens.Count != 2)
    throw new InvalidOperationException(); // No exception thrown

(Relatedly, see the Json.NET issue Provide a way to do case-sensitive property deserialization which requests a case-sensitive contract resolver for consistency with the case-sensitivity of LINQ-to-JSON.)