Add SelectMany extension method for Json (#859)

* Add SelectMany extension method for Json

* --

src/System.Linq.Dynamic.Core.NewtonsoftJson/NewtonsoftJsonExtensions.cs

@@ -2,7 +2,6 @@
 using System.Linq.Dynamic.Core.NewtonsoftJson.Config;
 using System.Linq.Dynamic.Core.NewtonsoftJson.Extensions;
 using System.Linq.Dynamic.Core.Validation;
-using System.Linq.Expressions;
 using Newtonsoft.Json.Linq;
 
 namespace System.Linq.Dynamic.Core.NewtonsoftJson;
@@ -550,7 +549,7 @@ public static JArray Select(this JArray source, NewtonsoftJsonParsingConfig conf
 
         if (source.Count == 0)
         {
-            return new JArray();
+            return [];
         }
 
         var queryable = ToQueryable(source, config);
@@ -591,6 +590,43 @@ public static JArray Select(this JArray source, Type resultType, string selector
     }
     #endregion Select
 
+    #region SelectMany
+    /// <summary>
+    /// Projects each element of a sequence to an <see cref="JArray"/> and combines the resulting sequences into one sequence.
+    /// </summary>
+    /// <param name="source">A sequence of values to project.</param>
+    /// <param name="selector">A projection string expression to apply to each element.</param>
+    /// <param name="args">An object array that contains zero or more objects to insert into the predicate as parameters. Similar to the way String.Format formats strings.</param>
+    /// <returns>A <see cref="JArray"/> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.</returns>
+    public static JArray SelectMany(this JArray source, string selector, params object?[] args)
+    {
+        return SelectMany(source, NewtonsoftJsonParsingConfig.Default, selector, args);
+    }
+
+    /// <summary>
+    /// Projects each element of a sequence to an <see cref="JArray"/> and combines the resulting sequences into one sequence.
+    /// </summary>
+    /// <param name="source">A sequence of values to project.</param>
+    /// <param name="config">The <see cref="NewtonsoftJsonParsingConfig"/>.</param>
+    /// <param name="selector">A projection string expression to apply to each element.</param>
+    /// <param name="args">An object array that contains zero or more objects to insert into the predicate as parameters. Similar to the way String.Format formats strings.</param>
+    /// <returns>A <see cref="JArray"/> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.</returns>
+    public static JArray SelectMany(this JArray source, NewtonsoftJsonParsingConfig config, string selector, params object?[] args)
+    {
+        Check.NotNull(source);
+        Check.NotNull(config);
+        Check.NotNullOrEmpty(selector);
+
+        if (source.Count == 0)
+        {
+            return [];
+        }
+
+        var queryable = ToQueryable(source, config);
+        return ToJArray(() => queryable.SelectMany(config, selector, args));
+    }
+    #endregion SelectMany
+
     #region Single
     /// <summary>
     /// Returns the only element of a sequence that satisfies a specified condition, and throws an exception if there

src/System.Linq.Dynamic.Core.SystemTextJson/SystemTextJsonExtensions.cs

@@ -4,7 +4,6 @@
 using System.Linq.Dynamic.Core.SystemTextJson.Extensions;
 using System.Linq.Dynamic.Core.SystemTextJson.Utils;
 using System.Linq.Dynamic.Core.Validation;
-using System.Linq.Expressions;
 using System.Text.Json;
 
 namespace System.Linq.Dynamic.Core.SystemTextJson;
@@ -676,7 +675,7 @@ public static JsonDocument Select(this JsonDocument source, string selector, par
     /// <param name="config">The <see cref="SystemTextJsonParsingConfig"/>.</param>
     /// <param name="selector">A projection string expression to apply to each element.</param>
     /// <param name="args">An object array that contains zero or more objects to insert into the predicate as parameters.</param>
-    /// <returns>An <see cref="JsonElement"/> whose elements are the result of invoking a projection string on each element of source.</returns>
+    /// <returns>An <see cref="JsonDocument"/> whose elements are the result of invoking a projection string on each element of source.</returns>
     public static JsonDocument Select(this JsonDocument source, SystemTextJsonParsingConfig config, string selector, params object?[] args)
     {
         Check.NotNull(source);
@@ -721,6 +720,38 @@ public static JsonDocument Select(this JsonDocument source, Type resultType, str
     }
     #endregion Select
 
+    #region SelectMany
+    /// <summary>
+    /// Projects each element of a sequence to an <see cref="JsonDocument"/> and combines the resulting sequences into one sequence.
+    /// </summary>
+    /// <param name="source">The source <see cref="JsonDocument"/></param>
+    /// <param name="selector">A projection string expression to apply to each element.</param>
+    /// <param name="args">An object array that contains zero or more objects to insert into the predicate as parameters. </param>
+    /// <returns>A <see cref="JsonDocument"/> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.</returns>
+    public static JsonDocument SelectMany(this JsonDocument source, string selector, params object?[] args)
+    {
+        return SelectMany(source, SystemTextJsonParsingConfig.Default, selector, args);
+    }
+
+    /// <summary>
+    /// Projects each element of a sequence to an <see cref="JsonDocument"/> and combines the resulting sequences into one sequence.
+    /// </summary>
+    /// <param name="source">The source <see cref="JsonDocument"/></param>
+    /// <param name="config">The <see cref="SystemTextJsonParsingConfig"/>.</param>
+    /// <param name="selector">A projection string expression to apply to each element.</param>
+    /// <param name="args">An object array that contains zero or more objects to insert into the predicate as parameters.</param>
+    /// <returns>A <see cref="JsonDocument"/> whose elements are the result of invoking a one-to-many projection function on each element of the input sequence.</returns>
+    public static JsonDocument SelectMany(this JsonDocument source, SystemTextJsonParsingConfig config, string selector, params object?[] args)
+    {
+        Check.NotNull(source);
+        Check.NotNull(config);
+        Check.NotNullOrEmpty(selector);
+
+        var queryable = ToQueryable(source, config);
+        return ToJsonDocumentArray(() => queryable.SelectMany(config, selector, args));
+    }
+    #endregion SelectMany
+
     #region Single
     /// <summary>
     /// Returns the only element of a sequence, and throws an exception if there

test/System.Linq.Dynamic.Core.NewtonsoftJson.Tests/NewtonsoftJsonTests.cs

@@ -323,6 +323,37 @@ public void Select_ResultType()
         array.Should().ContainInOrder(1, 4, 9);
     }
 
+    [Fact]
+    public void SelectMany()
+    {
+        // Arrange
+        var json =
+        """
+           [{
+               "PhoneNumbers": [
+                   { "Number": "123" },
+                   { "Number": "456" }
+               ]
+           },
+           {
+               "PhoneNumbers": [
+                   { "Number": "789" },
+                   { "Number": "012" }
+               ]
+           }]
+        """;
+        var source = JArray.Parse(json);
+
+        // Act
+        var result = source
+            .SelectMany("PhoneNumbers")
+            .Select("Number");
+
+        // Assert
+        var array = result.Select(x => x.Value<string>());
+        array.Should().BeEquivalentTo("123", "456", "789", "012");
+    }
+
     [Fact]
     public void Single()
     {

test/System.Linq.Dynamic.Core.SystemTextJson.Tests/SystemTextJsonTests.cs

@@ -320,6 +320,37 @@ public void Select()
         array.Should().BeEquivalentTo("John", "Doe");
     }
 
+    [Fact]
+    public void SelectMany()
+    {
+        // Arrange
+        var json =
+            """
+               [{
+                   "PhoneNumbers": [
+                       { "Number": "123" },
+                       { "Number": "456" }
+                   ]
+               },
+               {
+                   "PhoneNumbers": [
+                       { "Number": "789" },
+                       { "Number": "012" }
+                   ]
+               }]
+            """;
+        var source = JsonDocument.Parse(json);
+
+        // Act
+        var result = source
+            .SelectMany("PhoneNumbers")
+            .Select("Number");
+
+        // Assert
+        var array = result.RootElement.EnumerateArray().Select(x => x.GetString());
+        array.Should().BeEquivalentTo("123", "456", "789", "012");
+    }
+
     [Fact]
     public void Single()
     {