Fix duplicate properties from being mapped and ensure AutoMap is idempotent

Closes #1852

Author: gmarz

src/Nest/CommonAbstractions/SerializationBehavior/GenericJsonConverters/VerbatimDictionaryKeysConverter.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Collections;
 using System.Collections.Generic;
 using System.Globalization;
@@ -24,13 +25,13 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
 
 		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
 		{
-
 			var dictionary = value as IDictionary;
 			if (dictionary == null) return;
 
 			var settings = serializer.GetConnectionSettings();
 
-			writer.WriteStartObject();
+			var seenEntries = new Dictionary<string, object>();
+
 			foreach (DictionaryEntry entry in dictionary)
 			{
 				if (entry.Value == null && serializer.NullValueHandling == NullValueHandling.Ignore)
@@ -64,11 +65,15 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
 				else
 					key = Convert.ToString(entry.Key, CultureInfo.InvariantCulture);
 
-				writer.WritePropertyName(key);
-				serializer.Serialize(writer, entry.Value);
-
+				seenEntries[key] = entry.Value;
 			}
 
+			writer.WriteStartObject();
+			foreach(var entry in seenEntries)
+			{
+				writer.WritePropertyName(entry.Key);
+				serializer.Serialize(writer, entry.Value);
+			}
 			writer.WriteEndObject();
 		}
 	}

src/Nest/Indices/MappingManagement/PutMapping/PutMappingRequest.cs

@@ -135,13 +135,8 @@ public PutMappingDescriptor(IndexName index, TypeName type) : base(r=>r.Required
 		/// <pre>Class types default to object and Enums to int</pre>
 		/// <pre>Later calls can override whatever is set is by this call.</pre>
 		/// </summary>
-		public PutMappingDescriptor<T> AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) => Assign(a =>
-		{
-			a.Properties = a.Properties ?? new Properties();
-			var autoProperties = new PropertyWalker(typeof(T), visitor, maxRecursion).GetProperties();
-			foreach (var autoProperty in (IEnumerable<KeyValuePair<PropertyName, IProperty>>)autoProperties)
-				a.Properties[autoProperty.Key] = autoProperty.Value;
-		});
+		public PutMappingDescriptor<T> AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) =>
+			Assign(a => a.Properties = a.Properties.AutoMap<T>(visitor, maxRecursion));
 
 		/// <inheritdoc/>
 		public PutMappingDescriptor<T> AutoMap(int maxRecursion) => AutoMap(null, maxRecursion);

src/Nest/Mapping/TypeMapping.cs

@@ -140,8 +140,8 @@ public class TypeMappingDescriptor<T> : DescriptorBase<TypeMappingDescriptor<T>,
 		/// <pre>Class types default to object and Enums to int</pre>
 		/// <pre>Later calls can override whatever is set is by this call.</pre>
 		/// </summary>
-		public TypeMappingDescriptor<T> AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) => 
-			Assign(a => a.Properties = new PropertyWalker(typeof(T), visitor, maxRecursion).GetProperties());
+		public TypeMappingDescriptor<T> AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) =>
+			Assign(a => a.Properties = a.Properties.AutoMap<T>(visitor, maxRecursion));
 
 		/// <inheritdoc/>
 		public TypeMappingDescriptor<T> AutoMap(int maxRecursion) => AutoMap(null, maxRecursion);

src/Nest/Mapping/Types/Complex/Object/ObjectProperty.cs

@@ -83,13 +83,8 @@ public TDescriptor Path(string path) =>
 		public TDescriptor Properties(Func<PropertiesDescriptor<TChild>, IPromise<IProperties>> selector) =>
 			Assign(a => a.Properties = selector?.Invoke(new PropertiesDescriptor<TChild>(a.Properties))?.Value);
 
-		public TDescriptor AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) => Assign(a =>
-		{
-			a.Properties = a.Properties ?? new Properties();
-			var autoProperties = new PropertyWalker(typeof(TChild), visitor, maxRecursion).GetProperties();
-			foreach (var autoProperty in (IEnumerable<KeyValuePair<PropertyName, IProperty>>)autoProperties)
-				a.Properties[autoProperty.Key] = autoProperty.Value;
-		});
+		public TDescriptor AutoMap(IPropertyVisitor visitor = null, int maxRecursion = 0) =>
+			Assign(a => a.Properties = a.Properties.AutoMap<TChild>(visitor, maxRecursion));
 
 		public TDescriptor AutoMap(int maxRecursion) => AutoMap(null, maxRecursion);
 	}

src/Nest/Mapping/Types/Properties.cs

@@ -113,4 +113,25 @@ private PropertiesDescriptor<T> SetProperty(IProperty type)
 			return this.Assign(a => a[type.Name] = type);
 		}
 	}
+
+	internal static class PropertiesExtensions
+	{
+		internal static IProperties AutoMap<T>(this IProperties existingProperties, IPropertyVisitor visitor = null, int maxRecursion = 0)
+			where T : class
+		{
+			var properties = new Properties();
+			var autoProperties = new PropertyWalker(typeof(T), visitor, maxRecursion).GetProperties();
+			foreach (var autoProperty in (IEnumerable<KeyValuePair<PropertyName, IProperty>>)autoProperties)
+				properties[autoProperty.Key] = autoProperty.Value;
+
+			// Existing/manually mapped properties always take precedence
+			if (existingProperties != null)
+			{
+				foreach (var existing in (IEnumerable<KeyValuePair<PropertyName, IProperty>>)existingProperties)
+					properties[existing.Key] = existing.Value;
+			}
+
+			return properties;
+		}
+	}
 }