NullableSerializer.cs

/* Copyright 2010-present MongoDB Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

using System;

namespace MongoDB.Bson.Serialization.Serializers
{
    /// <summary>
    /// An interface used by the LINQ3 translators to access the value serializer without needing to use reflection.
    /// </summary>
    public interface INullableSerializer
    {
        /// <summary>
        /// Gets the value serializer.
        /// </summary>
        IBsonSerializer ValueSerializer { get; }
    }

    /// <summary>
    /// Static factory class for NullableSerializers.
    /// </summary>
    public static class NullableSerializer
    {
        private readonly static IBsonSerializer __nullableBooleanInstance = new NullableSerializer<bool>(BooleanSerializer.Instance);
        private readonly static IBsonSerializer __nullableDecimalInstance = new NullableSerializer<decimal>(DecimalSerializer.Instance);
        private readonly static IBsonSerializer __nullableDecimal128Instance = new NullableSerializer<Decimal128>(Decimal128Serializer.Instance);
        private readonly static IBsonSerializer __nullableDoubleInstance = new NullableSerializer<double>(DoubleSerializer.Instance);
        private readonly static IBsonSerializer __nullableInt32Instance = new NullableSerializer<int>(Int32Serializer.Instance);
        private readonly static IBsonSerializer __nullableInt64Instance = new NullableSerializer<long>(Int64Serializer.Instance);
        private readonly static IBsonSerializer __nullableLocalDateTimeInstance = new NullableSerializer<DateTime>(DateTimeSerializer.LocalInstance);
        private readonly static IBsonSerializer __nullableObjectIdInstance = new NullableSerializer<ObjectId>(ObjectIdSerializer.Instance);
        private readonly static IBsonSerializer __nullableSingleInstance = new NullableSerializer<float>(SingleSerializer.Instance);
        private readonly static IBsonSerializer __nullableStandardGuidInstance = new NullableSerializer<Guid>(GuidSerializer.StandardInstance);
        private readonly static IBsonSerializer __nullableUtcDateTimeInstance = new NullableSerializer<DateTime>(DateTimeSerializer.UtcInstance);

        /// <summary>
        /// Gets a serializer for nullable bools.
        /// </summary>
        public static IBsonSerializer NullableBooleanInstance => __nullableBooleanInstance;

        /// <summary>
        /// Gets a serializer for nullable decimals.
        /// </summary>
        public static IBsonSerializer NullableDecimalInstance => __nullableDecimalInstance;

        /// <summary>
        /// Gets a serializer for nullable Decimal128s.
        /// </summary>
        public static IBsonSerializer NullableDecimal128Instance => __nullableDecimal128Instance;

        /// <summary>
        /// Gets a serializer for nullable doubles.
        /// </summary>
        public static IBsonSerializer NullableDoubleInstance => __nullableDoubleInstance;

        /// <summary>
        /// Gets a serializer for nullable ints.
        /// </summary>
        public static IBsonSerializer NullableInt32Instance => __nullableInt32Instance;

        /// <summary>
        /// Gets a serializer for nullable longs.
        /// </summary>
        public static IBsonSerializer NullableInt64Instance => __nullableInt64Instance;

        /// <summary>
        /// Gets a serializer for local DateTime.
        /// </summary>
        public static IBsonSerializer NullableLocalDateTimeInstance => __nullableLocalDateTimeInstance;

        /// <summary>
        /// Gets a serializer for nullable floats.
        /// </summary>
        public static IBsonSerializer NullableSingleInstance => __nullableSingleInstance;

        /// <summary>
        /// Gets a serializer for nullable ObjectIds.
        /// </summary>
        public static IBsonSerializer NullableObjectIdInstance => __nullableObjectIdInstance;

        /// <summary>
        /// Gets a serializer for nullable Guids with standard representation.
        /// </summary>
        public static IBsonSerializer NullableStandardGuidInstance => __nullableStandardGuidInstance;

        /// <summary>
        /// Gets a serializer for UTC DateTime.
        /// </summary>
        public static IBsonSerializer NullableUtcDateTimeInstance => __nullableUtcDateTimeInstance;

        /// <summary>
        /// Creates a NullableSerializer.
        /// </summary>
        /// <param name="valueSerializer">The value serializer.</param>
        /// <returns>A NullableSerializer</returns>
        public static IBsonSerializer Create(IBsonSerializer valueSerializer)
        {
            var valueType = valueSerializer.ValueType;
            var nullableSerializerType = typeof(NullableSerializer<>).MakeGenericType(valueType);
            return (IBsonSerializer)Activator.CreateInstance(nullableSerializerType, valueSerializer);
        }
    }

    /// <summary>
    /// Represents a serializer for nullable values.
    /// </summary>
    /// <typeparam name="T">The underlying type.</typeparam>
    public sealed class NullableSerializer<T> :
        SerializerBase<Nullable<T>>,
        IChildSerializerConfigurable,
        INullableSerializer
            where T : struct
    {
        // private fields
        private Lazy<IBsonSerializer<T>> _lazySerializer;

        // constructors
        /// <summary>
        /// Initializes a new instance of the <see cref="NullableSerializer{T}"/> class.
        /// </summary>
        public NullableSerializer()
            : this(BsonSerializer.SerializerRegistry)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="NullableSerializer{T}"/> class.
        /// </summary>
        /// <param name="serializer">The serializer.</param>
        public NullableSerializer(IBsonSerializer<T> serializer)
        {
            if (serializer == null)
            {
                throw new ArgumentNullException("serializer");
            }

            _lazySerializer = new Lazy<IBsonSerializer<T>>(() => serializer);
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="NullableSerializer{T}" /> class.
        /// </summary>
        /// <param name="serializerRegistry">The serializer registry.</param>
        public NullableSerializer(IBsonSerializerRegistry serializerRegistry)
        {
            if (serializerRegistry == null)
            {
                throw new ArgumentNullException("serializerRegistry");
            }

            _lazySerializer = Lazy.CreatePublicationOnly(() => serializerRegistry.GetSerializer<T>());
        }

        // public properties
        /// <summary>
        /// Gets the value serializer.
        /// </summary>
        public IBsonSerializer<T> ValueSerializer => _lazySerializer.Value;

        // explicitly implemented properties
        IBsonSerializer INullableSerializer.ValueSerializer => ValueSerializer;

        // public methods
        /// <summary>
        /// Deserializes a value.
        /// </summary>
        /// <param name="context">The deserialization context.</param>
        /// <param name="args">The deserialization args.</param>
        /// <returns>A deserialized value.</returns>
        public override T? Deserialize(BsonDeserializationContext context, BsonDeserializationArgs args)
        {
            var bsonReader = context.Reader;

            var bsonType = bsonReader.GetCurrentBsonType();
            if (bsonType == BsonType.Null)
            {
                bsonReader.ReadNull();
                return null;
            }
            else
            {
                return _lazySerializer.Value.Deserialize(context);
            }
        }

        /// <inheritdoc/>
        public override bool Equals(object obj)
        {
            if (object.ReferenceEquals(obj, null)) { return false; }
            if (object.ReferenceEquals(this, obj)) { return true; }
            return
                base.Equals(obj) &&
                obj is NullableSerializer<T> other &&
                object.Equals(_lazySerializer.Value, other._lazySerializer.Value);
        }

        /// <inheritdoc/>
        public override int GetHashCode() => 0;

        /// <summary>
        /// Serializes a value.
        /// </summary>
        /// <param name="context">The serialization context.</param>
        /// <param name="args">The serialization args.</param>
        /// <param name="value">The object.</param>
        public override void Serialize(BsonSerializationContext context, BsonSerializationArgs args, T? value)
        {
            var bsonWriter = context.Writer;

            if (value == null)
            {
                bsonWriter.WriteNull();
            }
            else
            {
                _lazySerializer.Value.Serialize(context, value.Value);
            }
        }

        /// <summary>
        /// Returns a serializer that has been reconfigured with the specified serializer.
        /// </summary>
        /// <param name="serializer">The serializer.</param>
        /// <returns>
        /// The reconfigured serializer.
        /// </returns>
        public NullableSerializer<T> WithSerializer(IBsonSerializer<T> serializer)
        {
            if (serializer == _lazySerializer.Value)
            {
                return this;
            }
            else
            {
                return new NullableSerializer<T>(serializer);
            }
        }

        // explicit interface implementations
        IBsonSerializer IChildSerializerConfigurable.ChildSerializer
        {
            get { return _lazySerializer.Value; }
        }

        IBsonSerializer IChildSerializerConfigurable.WithChildSerializer(IBsonSerializer childSerializer)
        {
            return WithSerializer((IBsonSerializer<T>)childSerializer);
        }
    }
}