DbAttribute

.NET Customisation User Guide

.NET Customisation : Database Interface : Data Model Definition Classes : DbAttribute

This is very similar to DbElementType. There is a single class for all attributes.

The purpose of the class is to:

•

Access the metadata (i.e. data about data) associated with attributes, for example: type, name, length.

•

Identify attributes. i.e. methods on other classes should always take a DbAttribute rather than a string as an argument to denote the attribute. Any comparison of attribute identity should be done by comparing DbAttribute objects.

The class should not be confused with the attribute value. The actual Attribute value for a particular Element can only be accessed via the DbElement class. Comparing two DbAttributes just compares whether they identify the same attribute, the comparison does not look at attribute values in any way.

External to the AVEVA module, the hash value can be used to uniquely identify an Attribute. The hash value is a 32 bit integer.

In C# a DbAttribute object may be obtained in the following ways:

1.

Use globally defined instances. Each attribute has a globally declared instance in the DbAttributeInstance class. This is the standard way of specifying an attribute.

2.

Look up the DbAttribute given the attribute name. This is only needed for UDAs, since all other attributes can be obtained from the global instances. The colon must be included as part of the name.

3.

Look up the DbAttribute given the attribute hash value. Generally this is only needed if reading the hash value from an external system.

4.

Various methods on other classes, such as DbElement, will return a list of DbAttributesTypes.

The methods allow the following metadata to be accessed:


Attribute Type
Units
Name
Description
Category
Size
Allowed Values
Allowed ranges
Is a UDA
Is a pseudo attribute
Whether the attribute may take a qualifier

Find the type of attribute XLEN. We use the global instance of XLEN on the DbAttributeInstance class.

using ATT=Aveva.Core.Database.DbAttributeInstance;

DbAttributeType  xlenTyp= ATT.XLEN.Type;


DbAttributeUnit -	Type of units, for example: distance or bore or none.
DbAttributeType –	Type of attribute. One of
	INTEGER = 1,
	DOUBLE = 2,
	BOOL = 3,
	STRING = 4,
	ELEMENT = 5,
	DIRECTION = 7,
	POSITION = 8,
	ORIENTATION = 9
DbAttributeQualifier – used to determine what sort of qualifier an attribute has

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