SqlNull.cs

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// 
//  Copyright 2010-2015 Deveel
// 
//    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;

using Deveel.Data.Serialization;

namespace Deveel.Data.Sql.Objects {
    [Serializable]
    public struct SqlNull : ISqlObject, IConvertible, ISerializable {
        public static readonly SqlNull Value = new SqlNull();

        private SqlNull(ObjectData data) {
        }

        int IComparable.CompareTo(object obj) {
            return (this as ISqlObject).CompareTo((ISqlObject) obj);
        }

        int IComparable<ISqlObject>.CompareTo(ISqlObject other) {
            throw new NotSupportedException();
        }

        public bool IsNull {
            get { return true; }
        }

        void ISerializable.GetData(SerializeData data) {
        }

        bool ISqlObject.IsComparableTo(ISqlObject other) {
            return false;
        }

        public override bool Equals(object obj) {
            if (obj is SqlNull)
                return true;
            if (obj is ISqlObject)
                return ((ISqlObject) obj).IsNull;

            return false;
        }

        public override int GetHashCode() {
            return 0;
        }

        public static bool operator ==(SqlNull a, ISqlObject b) {
            if (Equals(a, b))
                return true;
            if (b == null || b.IsNull)
                return true;

            return false;
        }

        public static bool operator !=(SqlNull a, ISqlObject b) {
            return !(a == b);
        }

        TypeCode IConvertible.GetTypeCode() {
            return TypeCode.Object;
        }

        bool IConvertible.ToBoolean(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        char IConvertible.ToChar(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        sbyte IConvertible.ToSByte(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        byte IConvertible.ToByte(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        short IConvertible.ToInt16(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        ushort IConvertible.ToUInt16(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        int IConvertible.ToInt32(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        uint IConvertible.ToUInt32(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        long IConvertible.ToInt64(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        ulong IConvertible.ToUInt64(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        float IConvertible.ToSingle(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        double IConvertible.ToDouble(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        decimal IConvertible.ToDecimal(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        DateTime IConvertible.ToDateTime(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        string IConvertible.ToString(IFormatProvider provider) {
            throw new InvalidCastException();
        }

        object IConvertible.ToType(Type conversionType, IFormatProvider provider) {
            throw new InvalidCastException();
        }

        public override string ToString() {
            return "NULL";
        }
    }
}