2.3 Datatypes

Data fetched from a database into a DBTools.h++ application may be stored internally by DBTools.h++ in instances of the RWDBValue class. Most applications can ignore RWDBValue and fetch data directly into C++ variables. If you do need to use it, Table 1 shows how Oracle datatypes are mapped into RWDBValues, and lists the C++ class or datatype appropriate for each Oracle datatype. See the Oracle Application Developer's Guide for more information on Oracle datatypes.

Table 1 -- Type mapping when retrieving data

Oracle Datatype	RWDBValue::ValueType	C++ Datatype
BLOB/CLOB	Not supported	Not supported
`CHAR(n) VARCHAR2(n)`	`String`	*RWCString*
`DATE`	`DateTime`	*RWDBDateTime*
`FLOAT(p)`	`Double`	`double`
`LONG`	`String`	*RWCString*
`MLSLABEL`	`String`	*RWCString*
`NCHAR(n)` `NVARCHAR2(n)`	`String`¹	*RWCString*²
`NUMBER(p,s)`	`Decimal`	*RWDecimalPortable*
`NUMBER(p,129)`	Double	`double`
For machines with a 32-bit long: `NUMBER(p,0) p<10` `NUMBER(p,0) p>=10`	`Long` `Decimal`	`long int` *RWDecimalPortable*
For machines with a 64-bit long: `NUMBER(p,0) p<19` `NUMBER(p,0) p>=19`	`Long` `Decimal`	`long int` *RWDecimalPortable*
`RAW(n), LONG RAW`	`Blob`	*RWDBBlob*
`ROWID`	`String`	*RWCString*

1	Oracle doesn't differentiate when returning standard and national character strings. See Section 2.9.1 on return types.
2	See the previous footnote.

When an application uses DBTools.h++ to create an Oracle table, RWDBValue::ValueType is used to define the table's schema. Table 2 shows how DBTools.h++ maps its datatypes to Oracle datatypes when defining a schema.

Table 2 -- Type mapping when creating tables

RWDBValue::ValueType	Oracle datatype
`Blob`	`RAW(n)` if `length` <= 255, otherwise `LONG` `RAW`
`Char`, `UnsignedChar`	`NUMBER(38,0)`
`Date`	`DATE`
`DateTime`	`DATE`
`Decimal`	`NUMBER(p,s)` using `precision` and `scale` of column
`Double`	`FLOAT(126)`
`Duration`	Not supported by Oracle
`Float`	`FLOAT(p)` using `precision` of column
`Int`, `UnsignedInt`	`NUMBER(d)`, where `d` is the number of digits needed to store the maximum value an `int` can express on the client machine
`Long`, `UnsignedLong`	`NUMBER(d)`, where `d` is the number of digits needed to store the maximum value a `long` can express on the client machine
`MBString`, `WString`	`NVARCHAR2`
`Short`, `UnsignedShort`	`NUMBER(d)`, where `d` is the number of digits needed to store the maximum value a short can express on the client machine
`String`	`VARCHAR` if `length` is <= 2000, otherwise `LONG`

2.3.1 Restrictions on the Use of Datatypes

Oracle OCI and servers place restrictions on the use of certain datatypes. Where possible, DBTools.h++ tries to be flexible about datatypes. However, there are some situations where conversions are not possible, and in these cases your application will need to be aware of the contexts in which certain datatypes can be used Table 3 outlines the restrictions associated with each DBTools.h++ type.

Table 3 -- Restrictions on the use of DBTools.h++ datatypes

RWDBValue::ValueType	Restrictions
`Blob`	No restrictions.
`Char`, `UnsignedChar`	No restrictions.
`Date`	No restrictions.
`DateTime`	No restrictions.
`Decimal`	No restrictions.
`Double`	No restrictions.
`Duration`	*Not supported by Oracle
`Float`	No restrictions.
`Int`, `UnsignedInt`	No restrictions.
`Long`, `UnsignedLong`	No restrictions.
`MBString`, `WString`	Limited to 2,000 bytes
`Short`, `UnsignedShort`	No restrictions.
`String`	No restrictions.