MySQL :: MySQL NDB Cluster API Developer Guide :: 2.3.21 The NdbRecAttr Class

NdbRecAttr Class Overview

Parent class

None

Child classes

None

Description

NdbRecAttr contains the value of an attribute. An NdbRecAttr object is used to store an attribute value after it has been retrieved using the NdbOperation::getValue() method. This object is allocated by the NDB API. A brief example is shown here:

MyRecAttr = MyOperation->getValue("ATTR2", NULL);

if(MyRecAttr == NULL)
  goto error;

if(MyTransaction->execute(Commit) == -1)
  goto error;

ndbout << MyRecAttr->u_32_value();

For additional examples, see Section 2.5.2, “NDB API Example Using Synchronous Transactions”.

An NdbRecAttr object is instantiated with its value only when NdbTransaction::execute() is invoked. Prior to this, the value is undefined. (Use NdbRecAttr::isNULL() to check whether the value is defined.) This means that an NdbRecAttr object has valid information only between the times that NdbTransaction::execute() and Ndb::closeTransaction() are called. The value of the NULL indicator is -1 until the NdbTransaction::execute() method is invoked.

Methods

NdbRecAttr has a number of methods for retrieving values of various simple types directly from an instance of this class.

It is also possible to obtain a reference to the value regardless of its actual type, by using NdbRecAttr::aRef(); however, you should be aware that this is not type-safe, and requires a cast from the user.

The following table lists all of the public methods of this class and the purpose or use of each method:

Table 2.57 NdbRecAttr class methods and descriptions

Name	Description
`~NdbRecAttr()`	Destructor method
`aRef()`	Gets a pointer to the attribute value
`char_value()`	Retrieves a `Char` attribute value
`clone()`	Makes a deep copy of the `RecAttr` object
`double_value()`	Retrieves a `Double` attribute value, as a double (8 bytes)
`float_value()`	Retrieves a `Float` attribute value, as a float (4 bytes)
`get_size_in_bytes()`	Gets the size of the attribute, in bytes
`getColumn()`	Gets the column to which the attribute belongs
`getType()`	Gets the attribute's type (`Column::Type`)
`isNULL()`	Tests whether the attribute is `NULL`
`int8_value()`	Retrieves a `Tinyint` attribute value, as an 8-bit integer
`int32_value()`	Retrieves an `Int` attribute value, as a 32-bit integer
`int64_value()`	Retrieves a `Bigint` attribute value, as a 64-bit integer
`medium_value()`	Retrieves a `Mediumint` attribute value, as a 32-bit integer
`short_value()`	Retrieves a `Smallint` attribute value, as a 16-bit integer
`u_8_value()`	Retrieves a `Tinyunsigned` attribute value, as an unsigned 8-bit integer
`u_32_value()`	Retrieves an `Unsigned` attribute value, as an unsigned 32-bit integer
`u_64_value()`	Retrieves a `Bigunsigned` attribute value, as an unsigned 64-bit integer
`u_char_value()`	Retrieves a `Char` attribute value, as an unsigned `char`
`u_medium_value()`	Retrieves a `Mediumunsigned` attribute value, as an unsigned 32-bit integer
`u_short_value()`	Retrieves a `Smallunsigned` attribute value, as an unsigned 16-bit integer

The NdbRecAttr class has no public constructor; an instance of this object is created using NdbTransaction::execute(). For information about the destructor, which is public, see ~NdbRecAttr().

Types

The NdbRecAttr class defines no public types.

~NdbRecAttr()

Description

The NdbRecAttr class destructor method.

You should delete only copies of NdbRecAttr objects that were created in your application using the clone() method.

Signature

~NdbRecAttr
    (
      void
    )

Parameters

None.

Return value

None.

NdbRecAttr::aRef()

Description

This method is used to obtain a reference to an attribute value, as a char pointer. This pointer is aligned appropriately for the data type. The memory is released by the NDB API when NdbTransaction::close() is executed on the transaction which read the value.

Signature

char* aRef
    (
      void
    ) const

Parameters

A pointer to the attribute value. Because this pointer is constant, this method can be called anytime after NdbOperation::getValue() has been called.

Return value

None.

NdbRecAttr::char_value()

Description

This method gets a Char value stored in an NdbRecAttr object, and returns it as a char.

Signature

char char_value
    (
      void
    ) const

Parameters

None.

Return value