IMPLEMENTING A USER-DEFINED TYPE user-defined type could be

IMPLEMENTING A USER-DEFINED TYPE user-defined type could be used to represent a nail that will be sorted first on its Sizefield and second on its Pricefield. namespace UDT { [SqlUserDefinedType( Format=Format.Native, // SQL Server provides serialization code IsByteOrdered = true)] // Sorts and compares may be used [Serializable] // required for Native [StructLayout(LayoutKind.Sequential)] // required for Native public struct Nail … { int Size; // sort on Size first float Price // sort on Price second // implementation … } } Format = Format.Native is best practice when it can be used. There are two simple cases when it cannot be used. One is when the class requires a field of a type that is not allowed for Format.Native. The other is that you cannot achieve the sort order that you wish by just ordering the fields in the CLR class. A class that can t meet the requirements to use Native must use System.Data.Sql.Format.UserDefined. When Format is set to User Defined, the class implementing the user-defined type must provide the code to read and write the byte stream by implementing the IBinary Serialize interface. In addition, the UserDefined setting requires two other properties of SqlUserDefinedTypeAttribute to be set appropriately: the IsFixedLengthand MaxByteSizeproperties. The MaxByteSize property is used only when Format = Format. UserDefinedand indicates the maximum size of the byte stream, in bytes, used to save the user-defined type. It is desirable to keep this as small as possible. You will have to accurately determine this when you implement the IBinarySerializeinterface, which will be covered later. The IsFixedLength property is used only when Format = Format. UserDefined and is set to true if the size of the byte stream is always the same size as indicated by MaxByteSize; otherwise, it is set to false. SQL Server needs to know this because the way it allocates space on the disk differs depending on whether its size is fixed or not. In general, SQL Server can more efficiently manage a fixed size type better than one whose size varies.

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