CSHARP-1373: added $min expression support.

Author: craiggwilson

Docs/reference/content/reference/driver/expressions.md

@@ -754,6 +754,15 @@ p => p.FavoriteNumbers.Concat(new [] { 1, 2, 3 })
 { $concatArrays: ['$FavoriteNumbers', [1, 2, 3]] }
 ```
 
+#### $min
+
+```csharp
+p => p.FavoriteNumbers.Min()
+```
+```json
+{ $min: '$FavoriteNumbers' }
+```
+
 #### $size
 
 ```csharp

src/MongoDB.Driver.Tests/Linq/Translators/AggregateProjectTranslatorTests.cs

@@ -474,6 +474,28 @@ public async Task Should_translate_millisecond()
             result.Value.Result.Should().Be(16);
         }
 
+        [Test]
+        [RequiresServer(MinimumVersion = "3.1.7")]
+        public async Task Should_translate_min()
+        {
+            var result = await Project(x => new { Result = x.M.Min() });
+
+            result.Projection.Should().Be("{ Result: { \"$min\": \"$M\" }, _id: 0 }");
+
+            result.Value.Result.Should().Be(2);
+        }
+
+        [Test]
+        [RequiresServer(MinimumVersion = "3.1.7")]
+        public async Task Should_translate_min_with_selector()
+        {
+            var result = await Project(x => new { Result = x.G.Min(g => g.E.F) });
+
+            result.Projection.Should().Be("{ Result: { \"$min\": \"$G.E.F\" }, _id: 0 }");
+
+            result.Value.Result.Should().Be(33);
+        }
+
         [Test]
         public async Task Should_translate_minute()
         {

src/MongoDB.Driver/Linq/Translators/AggregateLanguageTranslator.cs

@@ -395,7 +395,8 @@ private BsonValue TranslatePipeline(PipelineExpression node)
                 TryTranslateAllResultOperator(node, out result) ||
                 TryTranslateAnyResultOperator(node, out result) ||
                 TryTranslateContainsResultOperator(node, out result) ||
-                TryTranslateCountResultOperator(node, out result))
+                TryTranslateCountResultOperator(node, out result) ||
+                TryTranslateMinResultOperator(node, out result))
             {
                 return result;
             }
@@ -623,6 +624,19 @@ private bool TryTranslateHashSetMethodCall(MethodCallExpression node, out BsonVa
             return false;
         }
 
+        private bool TryTranslateMinResultOperator(PipelineExpression node, out BsonValue result)
+        {
+            var resultOperator = node.ResultOperator as MinResultOperator;
+            if (resultOperator != null)
+            {
+                result = new BsonDocument("$min", TranslateValue(node.Source));
+                return true;
+            }
+
+            result = null;
+            return false;
+        }
+
         private bool TryTranslateStaticMathMethodCall(MethodCallExpression node, out BsonValue result)
         {
             result = null;