Using the Get Methods to Read Column Values

Using the Get* Methods to Read Column Values

Before I show you the other Get* methods that read column values, you need to know the standard C# types and the values they support. You need to know these so that you can understand the type compatibilities between C# and SQL Server shown later. Table 9.3 shows the standard C# types, along with the underlying .NET type and the values that can be stored in the C# type.

Table 9.3: STANDARD C# AND .NET TYPES

C# TYPE	.NET TYPE	VALUES
bool	Boolean	A Boolean true or false value.
byte	Byte	An 8-bit unsigned integer between 0 and 28 - 1(255).
char	Char	A 16-bit Unicode character.
DateTime	DateTime	A date and time between 12:00:00 AM January 1, 0001 and 11:59:59 PM December 31, 9999.
decimal	Decimal	A fixed precision and scale number between approximately +/-1.0 *10-28 and approximately +/-7.9 *1028 with 28 significant figures of precision.
double	Double	A 64-bit floating-point number between approximately +/-5 *10-324 and approximately +/-1.7 *10308 with 15 to 16 significant figures of precision.
float	Single	A 32-bit floating-point number between approximately +/-1.5 *10-45 to approximately +/-3.4 *1038 with 7 significant figures of precision.
Guid	Guid	A 128-bit unsigned integer value (16 bytes) that that is unique across all computers and networks.
int	Int32	A 32-bit signed integer between -231 (-2,147,483,648) and 231 - 1 (2,147,483,647).
long	Int64	A 64-bit signed integer between -263 (-9,223,372,036,854,775,808) and 263 - 1 (9,223,372,036,854,775,807).
sbyte	SByte	An 8-bit signed integer between -27 (-128) and 27 - 1 (127).
short	Int16	A 16-bit signed integer between -215 (-32,768) and 215 - 1 (32,767).
string	String	A variable-length string of 16-bit Unicode characters.
uint	UInt32	A 32-bit unsigned integer between 0 and 232 - 1 (4,294,967,295).
ulong	UInt64	A 64-bit unsigned integer between 0 and 264 - 1 (18,446,744,073,709,551,615).
ushort	UInt16	A 16-bit unsigned integer between 0 and 216 - 1 (65,535).

Note 

The standard C# types are defined in the System namespace.

Table 9.4 shows the SQL Server types, the compatible standard C# types, and the DataReader Get* methods that return each C# type. You use this table to figure out which method to call to get a specific column type. For example, if you need to get the value of a bigint column, you call the GetInt64() method that returns a long.

Table 9.4: SQL SERVER TYPES, COMPATIBLE STANDARD C# TYPES, AND GET* METHODS

SQL SERVER TYPE	COMPATIBLE STANDARD C# TYPE	GET* METHOD
binary	byte[]	GetBytes()
bigint	long	GetInt64()
bit	bool	GetBoolean()
char	string	GetString()
datetime	DateTime	GetDateTime()
decimal	decimal	GetDecimal()
float	double	GetDouble()
image	byte[]	GetBytes()
int	int	GetInt32()
money	decimal	GetDecimal()
nchar	string	GetString()
ntext	string	GetString()
nvarchar	string	GetString()
numeric	decimal	GetDecimal()
real	float	GetFloat()
smalldatetime	DateTime	GetDateTime()
smallint	short	GetInt16()
smallmoney	decimal	GetDecimal()
sql_varient	object	GetValue()
text	string	GetString()
timestamp	byte[]	GetBytes()
tinyint	byte	GetByte()
varbinary	byte[]	GetBytes()
varchar	string	GetString()
uniqueidentifier	Guid	GetGuid()

Note 

You can see the SQL Server types and the values supported by those types in Table 2.3 of Chapter 2, "Introduction to Databases."

Note 

The Get* methods are defined in all of the DataReader classes and work for all databases.

Next you'll see how to use some of the methods shown in Table 9.4.