C# BsonReader.GetBookmark方法代码示例

        // public methods
        /// <summary>
        /// Deserializes an object from a BsonReader.
        /// </summary>
        /// <param name="bsonReader">The BsonReader.</param>
        /// <param name="nominalType">The nominal type of the object.</param>
        /// <param name="options">The serialization options.</param>
        /// <returns>An object.</returns>
        public object Deserialize(BsonReader bsonReader, Type nominalType, IBsonSerializationOptions options)
        {
            if (nominalType != typeof(object))
            {
                var message = string.Format("ObjectSerializer can only be used with nominal type System.Object, not type {0}.", nominalType.FullName);
                throw new InvalidOperationException(message);
            }

            var bsonType = bsonReader.GetCurrentBsonType();
            if (bsonType == BsonType.Null)
            {
                bsonReader.ReadNull();
                return null;
            }
            else if (bsonType == BsonType.Document)
            {
                var bookmark = bsonReader.GetBookmark();
                bsonReader.ReadStartDocument();
                if (bsonReader.ReadBsonType() == BsonType.EndOfDocument)
                {
                    bsonReader.ReadEndDocument();
                    return new object();
                }
                else
                {
                    bsonReader.ReturnToBookmark(bookmark);
                }
            }

            var discriminatorConvention = BsonSerializer.LookupDiscriminatorConvention(typeof(object));
            var actualType = discriminatorConvention.GetActualType(bsonReader, typeof(object));
            if (actualType == typeof(object))
            {
                var message = string.Format("Unable to determine actual type of object to deserialize. NominalType is System.Object and BsonType is {0}.", bsonType);
                throw new FileFormatException(message);
            }

            var serializer = BsonSerializer.LookupSerializer(actualType);
            return serializer.Deserialize(bsonReader, nominalType, actualType, options);
        }

        // private methods
        private bool IsCSharpNullRepresentation(BsonReader bsonReader)
        {
            var bookmark = bsonReader.GetBookmark();
            bsonReader.ReadStartDocument();
            var bsonType = bsonReader.ReadBsonType();
            if (bsonType == BsonType.Boolean)
            {
                var name = bsonReader.ReadName();
                if (name == "_csharpnull" || name == "$csharpnull")
                {
                    var value = bsonReader.ReadBoolean();
                    if (value)
                    {
                        bsonType = bsonReader.ReadBsonType();
                        if (bsonType == BsonType.EndOfDocument)
                        {
                            bsonReader.ReadEndDocument();
                            return true;
                        }
                    }
                }
            }

            bsonReader.ReturnToBookmark(bookmark);
            return false;
        }

        // public methods
        /// <summary>
        /// Gets the actual type of an object by reading the discriminator from a BsonReader.
        /// </summary>
        /// <param name="bsonReader">The reader.</param>
        /// <param name="nominalType">The nominal type.</param>
        /// <returns>The actual type.</returns>
        public Type GetActualType(BsonReader bsonReader, Type nominalType)
        {
            // the BsonReader is sitting at the value whose actual type needs to be found
            var bsonType = bsonReader.GetCurrentBsonType();
            if (bsonReader.State == BsonReaderState.Value)
            {
                Type primitiveType = null;
                switch (bsonType)
                {
                    case BsonType.Boolean: primitiveType = typeof(bool); break;
                    case BsonType.Binary:
                        var bookmark = bsonReader.GetBookmark();
                        byte[] bytes;
                        BsonBinarySubType subType;
                        bsonReader.ReadBinaryData(out bytes, out subType);
                        if (subType == BsonBinarySubType.UuidStandard || subType == BsonBinarySubType.UuidLegacy)
                        {
                            primitiveType = typeof(Guid);
                        }
                        bsonReader.ReturnToBookmark(bookmark);
                        break;
                    case BsonType.DateTime: primitiveType = typeof(DateTime); break;
                    case BsonType.Double: primitiveType = typeof(double); break;
                    case BsonType.Int32: primitiveType = typeof(int); break;
                    case BsonType.Int64: primitiveType = typeof(long); break;
                    case BsonType.ObjectId: primitiveType = typeof(ObjectId); break;
                    case BsonType.String: primitiveType = typeof(string); break;
                }

                // Type.IsAssignableFrom is extremely expensive, always perform a direct type check before calling Type.IsAssignableFrom
                if (primitiveType != null && (primitiveType == nominalType || nominalType.IsAssignableFrom(primitiveType)))
                {
                    return primitiveType;
                }
            }

            if (bsonType == BsonType.Document)
            {
                // ensure KnownTypes of nominalType are registered (so IsTypeDiscriminated returns correct answer)
                BsonSerializer.EnsureKnownTypesAreRegistered(nominalType);

                // we can skip looking for a discriminator if nominalType has no discriminated sub types
                if (BsonSerializer.IsTypeDiscriminated(nominalType))
                {
                    var bookmark = bsonReader.GetBookmark();
                    bsonReader.ReadStartDocument();
                    var actualType = nominalType;
                    if (bsonReader.FindElement(_elementName))
                    {
                        var discriminator = BsonValue.ReadFrom(bsonReader);
                        if (discriminator.IsBsonArray)
                        {
                            discriminator = discriminator.AsBsonArray.Last(); // last item is leaf class discriminator
                        }
                        actualType = BsonSerializer.LookupActualType(nominalType, discriminator);
                    }
                    bsonReader.ReturnToBookmark(bookmark);
                    return actualType;
                }
            }

            return nominalType;
        }