Json.NET LINQ query for single JProperty on JArray of JObjects - linq

Question

I have a JArray with this configuration
[
{
"name" : "text",
"age" : 32
},
{
"name" : "text2",
"age" : 33
},
]
and I want to use LINQ query to select a JArray containing JObjects with just the key value of a specified given key.
For example:
GetCollectionOfPropertiesByKey("name");
this would result in:
[
{
"name" : "text"
},
{
"name" : "text2"
},
]
using the same logic,
GetCollectionOfPropertiesByKey("age");
would result in:
[
{
"age" : 32
},
{
"age" : 33
},
]

Answer 1

You didn't specify whether you needed case-invariant filtering for properties by name, so here is an extension method with an optional StringComparison argument:
public static class JsonExtensions
{
public static JArray GetCollectionOfPropertiesByKey(this JArray array, string key, StringComparison comparison = StringComparison.Ordinal)
{
if (array == null)
return null;
var query = array
// Filter out array items that are not objects
.OfType<JObject>()
// Select the value JToken with the specified key using the specified StringComparison
.Select(o => o.GetValue(key, comparison))
// Filter for null (property was not found)
.Where(v => v != null)
// And select a new JObject containing just the JPropery parent of the selected value
.Select(v => new JObject(v.Parent));
return new JArray(query);
}
}
If a case-insensitive match is required, pass StringComparison.OrdinalIgnoreCase.
Notes:
The query filters for all items in the input array that are of type JObject, then uses JObject.GetValue(String, StringComparison) to get the corresponding value by key name.
Then, if a value is found, it constructs a new JObject using the parent of the selected value, which should be a JProperty.
If case insensitivity is never required, you could simplify the query a bit by using JObject.Property(String) to get the JProperty by key name, and then constructing a JObject containing it, like so:
var query = array
// Filter out array items that are not objects
.OfType<JObject>()
// Select the JProperty with the specified key
.Select(o => o.Property(key))
// Filter for null (property was not found)
.Where(p => p != null)
// And select a new JObject with just this property
.Select(p => new JObject(p));
Sample working .Net fiddle.