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Represents a column within a table or schema, or a particular parameter of a stored procedure. More...
#include <rw/db/column.h>
RWDBColumn provides a way to refer to a particular column of a table or schema, or to a particular parameter of a stored procedure. An application obtains instances of RWDBColumn by indexing into an RWDBTable or RWDBSchema.
RWDBColumn instances may be used in expressions (see RWDBExpr), which in turn are used to build up encapsulated SQL objects such as RWDBSelector.
RWDBColumn instances are also used in RWDBSchema. An RWDBSchema is a collection of RWDBColumn objects used to describe a database table, view, or stored procedure. When used in this way, RWDBColumn stores several pieces of information:
NULL valuesIf no schema information has been obtained for the table containing a column, the column will contain default values. For Native Type, Storage Length, Precision, and Scale, this default value is RWDB_NO_TRAIT, and may be used in conditional expressions as follows:
RWDBTable myTable = myDbase.table("myTable"); ... ... RWDBColumn myColumn = myTable["someColumn"]; if( myColumn.scale() == RWDB_NO_TRAIT ) { // do something; }
RWDBColumn is designed around the Interface/Implementation paradigm. An RWDBColumn instance is an interface to a reference-counted implementation; copy constructors and assignment operators produce additional references to a shared implementation. Unlike many classes in the DB Interface Module, RWDBColumn implementations do not require database-specific variants.
Precision and scale are used when defining numeric data types. Each database applies these specifications to data types in a slightly different manner. For example, Sybase applies precision and scale to decimal and numeric data types, while Oracle applies precision and scale to numeric data types only.
The precision of a column defines the total precision of the data type. For decimal data types, this translates into the total number of base ten digits. For floating point data types, this translates into binary digits or size.
The scale of a column defines the precision of the fractional part of the data type. For decimal data types, this translates into the total number of digits following the decimal point.
Note that precision and scale are often optional for a data type and that many databases apply default sizes when precision and scale are not provided.
For applications written with the DB Interface Module, precision and scale should always be specified if an application will create columns of a certain precision and scale. A DB Access Module can either disregard or use the necessary information in order to create a column of the correct data type. Typically, precision and scale should always be given for decimal columns.
#include <rw/db/column.h> RWDBColumn c = myTable["columnName"];
RWDBColumn is commonly used to construct encapsulated SQL expressions that can in turn become part of encapsulated SQL statements like RWDBSelector, RWDBInserter, RWDBDeleter, and RWDBUpdater. For example, to create an encapsulation of the SQL statement:
UPDATE myTable SET myColumn = 10 WHERE myKey < 100
we would write:
RWDBTable myTable = myDbase.table("myTable"); RWDBUpdater upd = myTable.updater(); upd << myTable["myColumn"].assign(10); upd.where(myTable["myKey"] < 100);
Note that the index expressions myTable["myColumn"] and myTable["myKey"] result in the construction of RWDBColumn instances that are then used to construct instances of an RWDBAssignment and RWDBExpr, respectively.
For additional details, see RWDBExpr, RWDBAssignment, RWDBCriterion, RWDBSelector, RWDBInserter, RWDBUpdater, and RWDBDeleter.
RWDBColumn can be used to describe a parameter to a stored procedure. The ParamType enum describes the method of passing parameters between the application and the stored procedure. See RWDBStoredProc for more information.
| RWDBColumn::RWDBColumn | ( | ) |
Default constructor that creates a column whose status is RWDBStatus::notInitialized. This constructor is provided for convenience, for example, for declaring arrays of columns; valid columns are obtained by indexing into RWDBTable and RWDBSchema objects.
| RWDBColumn::RWDBColumn | ( | const RWDBColumn & | column | ) |
Copy constructor. The created RWDBColumn shares an implementation with column.
| void RWDBColumn::acquire | ( | ) | const |
Attempts to acquire the internal mutex lock. If the mutex is already locked by another thread, the function blocks until the mutex is released. This function can be called from a const object.
| RWDBAssignment RWDBColumn::assign | ( | const RWDBExpr & | expression | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | RWDBValueManip | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWBasicUString & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDBBlob & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDecimalPortable & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDBDuration & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDBDateTime & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDateTime & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWTime & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDate & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWWString & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWDBMBString & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const RWCString & | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const wchar_t * | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | const char * | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | long double | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | double | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | float | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | unsigned long long | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | long long | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | unsigned int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | unsigned long int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | long int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | unsigned short int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | short int | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | unsigned char | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBAssignment RWDBColumn::assign | ( | char | value | ) | const |
Returns an RWDBAssignment that represents an encapsulation of the SQL clause:
column = value
where column refers to self. Like the SQL SET clause, it is used only in the SQL UPDATE statement.
| RWDBCriterion RWDBColumn::between | ( | const RWDBExpr & | expression1, | |
| const RWDBExpr & | expression2 | |||
| ) | const |
Returns an RWDBCriterion that represents an encapsulation of the SQL clause:
column BETWEEN expression1 AND expression2
where column refers to self. An RWDBCriterion is an encapsulation of an SQL WHERE clause.
| RWDBColumn& RWDBColumn::clearTable | ( | ) |
Dissociates self from any table. Returns a reference to self.
| RWDBColumn RWDBColumn::clone | ( | ) | const |
Returns a deep copy of self.
| RWDBStatus::ErrorHandler RWDBColumn::errorHandler | ( | ) | const |
Returns the error handler attached to self.
| RWDBCriterion RWDBColumn::in | ( | const RWDBExpr & | expression | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the SQL phrase:
column IN expression
where column refers to self. An RWDBCriterion is an encapsulation of an SQL WHERE clause. For example, to produce the SQL clause:
col1 in (1, 2, 3)
you could write:
RWOrdered aCollection; RWDBCollectableExpr e1(RWDBExpr(1)); RWDBCollectableExpr e2(RWDBExpr(2)); RWDBCollectableExpr e3(RWDBExpr(3)); aCollection.insert(&e1); aCollection.insert(&e2); aCollection.insert(&e3); RWDBExpr e(aCollection); table["col1"].in(e);
Alternatively, you could write:
| bool RWDBColumn::isEquivalent | ( | const RWDBColumn & | column | ) | const |
Returns a boolean value indicating whether or not self and column are equivalent. Columns are equivalent if they have the same names and are associated with the same table.
| RWDBCriterion RWDBColumn::isNull | ( | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the SQL clause:
column IS NULL
where column refers to self. An RWDBCriterion is an encapsulation of an SQL WHERE clause.
| bool RWDBColumn::isValid | ( | ) | const |
Returns true if self's status is RWDBStatus::ok, otherwise false.
| RWDBCriterion RWDBColumn::leftOuterJoin | ( | const RWDBExpr & | expr | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the LEFT OUTER JOIN SQL phrase for non-ANSI-compliant databases. See the entry for RWDBJoinExpr regarding ANSI-compliant joins. Also see the Access Module guides to determine which version of join is supported. An RWDBCriterion is an encapsulation of an SQL WHERE clause.
| RWDBCriterion RWDBColumn::like | ( | const RWDBExpr & | expression | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the SQL clause:
column LIKE expression
where column refers to self. For example, to produce the SQL clause:
col1 LIKE "%object%"
you would write:
table["col1"].like("%object%");
| RWDBCriterion RWDBColumn::matchUnique | ( | const RWDBExpr & | expression | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the SQL clause:
column MATCH UNIQUE expression
where column refers to self. An RWDBCriterion is an encapsulation of an SQL WHERE clause.
| RWDBColumn& RWDBColumn::name | ( | const RWCString & | newName | ) |
Changes the name of this column to newName. Note that this does not change the definition of the column in the database. Returns a reference to self.
| RWCString RWDBColumn::name | ( | ) | const |
Returns the name of the column.
| RWDBColumn& RWDBColumn::nativeType | ( | int | newType | ) |
Changes the nativeType attribute of self to newType. Note that this does not change the definition of the column in the database. Returns a reference to self.
| int RWDBColumn::nativeType | ( | ) | const |
Returns a value indicating the data type of the column as specified by the database vendor, or RWDB_NO_TRAIT if this information is not available. The meaning of the value returned depends on the database vendor's definitions.
| RWDBColumn& RWDBColumn::nullAllowed | ( | bool | nullAllowed | ) |
Changes the value of self's nullAllowed attribute to the value of nullAllowed. Note that this does not change the definition of the column in the database. Returns a reference to self.
| bool RWDBColumn::nullAllowed | ( | ) | const |
Returns true if the database reports that a null value is allowed in this column, or if no schema information has been obtained. Otherwise returns false.
| RWDBColumn& RWDBColumn::operator= | ( | const RWDBColumn & | column | ) |
Assignment operator. Self shares an implementation with column. Returns a reference to self.
| RWDBColumn& RWDBColumn::paramType | ( | RWDBColumn::ParamType | newType | ) |
Changes the paramType attribute of self to newType. Note that this does not change the definition of the parameter in the database. Returns a reference to self.
| ParamType RWDBColumn::paramType | ( | ) | const |
Returns a value indicating the parameter type of the column.
| RWDBColumn& RWDBColumn::precision | ( | int | newPrecision | ) |
Changes the precision attribute of self to newPrecision. Note that this does not change the definition of the column in the database. Returns a reference to self.
| int RWDBColumn::precision | ( | ) | const |
Returns the precision of the column as reported by the database. If not applicable to this column, or if no schema information has been obtained, returns RWDB_NO_TRAIT.
| RWCString RWDBColumn::qualifiedName | ( | ) | const |
Returns the name of the column qualified with the tag of the RWDBTable to which the column is associated. For example:
RWDBColumn col1 = table["col1"]; cout << col1.qualifiedName();
would produce output something like t123.col1. If self is not associated with any table, an unqualified name is returned.
| void RWDBColumn::release | ( | ) | const |
Releases a previously acquired mutex. This function can be called from a const object.
| RWDBCriterion RWDBColumn::rightOuterJoin | ( | const RWDBExpr & | expr | ) | const |
Returns an RWDBCriterion that represents an encapsulation of the RIGHT OUTER JOIN SQL phrase for non-ANSI-compliant databases. See the entry for RWDBJoinExpr regarding ANSI-compliant joins. Also see the Access Module guides to determine which version of join is supported. This function can be called from a const object. An RWDBCriterion is an encapsulation of an SQL WHERE clause.
| RWDBColumn& RWDBColumn::scale | ( | int | newScale | ) |
Changes the scale attribute of self to newScale. Note that this does not change the definition of the column in the database. Returns a reference to self.
| int RWDBColumn::scale | ( | ) | const |
Returns the scale of the column as reported by the database. If not applicable to this column, or if no schema information has been obtained, this routine returns RWDB_NO_TRAIT.
| void RWDBColumn::setErrorHandler | ( | RWDBStatus::ErrorHandler | handler | ) |
Installs handler as the error handler for self. By default, an RWDBStatus::ErrorHandler is inherited from the object that produced self; this method overrides the default.
| RWDBStatus RWDBColumn::status | ( | ) | const |
Returns the status of self.
| RWDBColumn& RWDBColumn::storageLength | ( | long | newLength | ) |
Changes the storageLength attribute of self to newLength. Note that this does not change the definition of the column in the database. Returns a reference to self.
| long RWDBColumn::storageLength | ( | ) | const |
Returns the length of the column as reported by the database. This is often used to obtain the maximum string length. If no schema information has been obtained, returns RWDB_NO_TRAIT.
| RWDBColumn& RWDBColumn::table | ( | const RWDBTable & | table | ) |
Changes the table attribute of self to table, thus associating the column with table. Returns a reference to self.
| RWDBTable RWDBColumn::table | ( | ) | const |
Returns the table with which self is associated, or a table whose status is RWDBStatus::notInitialized if self is not associated with a table.
| RWDBColumn& RWDBColumn::type | ( | RWDBValue::ValueType | newType | ) |
Changes the data type attribute of self to newType. Note that this does not change the definition of the column in the database. Returns a reference to self.
| RWDBValue::ValueType RWDBColumn::type | ( | ) | const |
Returns the data type used by the DB Interface Module to store this column's data; see RWDBValue for a list of valid types. If the type is not yet known, returns RWDBValue::NoType.
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