Adding Pseudo Attribute Code

Code can be plugged in to calculate the value of pseudo attributes. The code to do this must be registered in PDMS/Marine by passing in a C# delegate.

Code can be registered in two ways:

1. Against a specific UDA. The code will then be invoked for all elements having this UDA.

2. Against a specific UDA and a specific element type. The code will only be invoked for all elements of that type.

The same UDA may have multiple delegates registered for different element types.

There is a different delegate for each attribute type. for example, for integer attributes the delegate is:

public delegate double GetDoubleDelegate(DbElement ele, DbAttribute att, int qualifier);

These are defined in the DbPseudoAttribute class.

The user must write a method that matches the method signature of the delegate. for example, to write pseudo attribute code for a 'double' attribute, the user must write a method that has the signature defined by 'GetDoubleDelegate'. that means, a method that takes a DbElement, a DbAttribute, int and returns a double.

For example, the following method would be valid:

// Double delegate for UDA

static private double VolumeCalculation(DbElement ele,DbAttribute

att,int qualifier)

{

// calculate the volume by multiplying the lengths along each side

double x=ele.GetDouble(ATT.XLEN);

double y=ele.GetDouble(ATT.YLEN);

double z=ele.GetDouble(ATT.ZLEN);

// Result of UDA must be returned

return (x * y * z);

}

An instance of the delegate containing the method must then be created and registered with PDMS/Marine.

There are separate methods to register the different types of delegates. There are also separate methods to add a plugger for a particular element type. for example, the two methods to add a GetDoubleDelegate are:

public static void AddGetDoubleAttribute(DbAttribute att,GetIntDelegate plug)

public static void AddGetDoubleAttribute(DbAttribute att, DbElementType type, GetIntDelegate plug)

An example of registering a delegate is:

using System;

using NOUN=Aveva.Pdms.Database.DbElementTypeInstance;

using Ps=Aveva.Pdms.Database.DbPseudoAttribute;

namespace Aveva.PDMS.Shared.Tests

{

static public void RegisterDelegate()

{

// get uda attribute

DbAttribute uda=DbAttribute.GetDbAttribute(":VOLUME");

// Create instance of delegate containing "VolumeCalculation" method

Ps.GetDoubleDelegate dele=new Ps.GetDoubleDelegate(VolumeCal\-culation);

// Pass delegate instance to core PDMS. This will be invoked later

// when :VOLUME is queried.

// In this case registry for all valid element types.

Ps.AddGetDoubleAttribute(uda,dele);

}

}

Code may be plugged by UDET as well as the base type. The following criteria are used to locate the right plugged code:

3. If a UDET, look for a delegate plugged by UDET and attribute.

4. Look for a delegate plugged by base type and attribute

5. Look for a delegate plugged by matching attribute only.

For example, you could add three delegates to calculate :WEIGHT. You could add one that calculates the :WEIGHT on a :MYELE, one that calculates the :WEIGHT of SCTN and one that calculates WEIGHT for any other element for which :WEIGHT is valid.

A delegate only needs adding once at start up.

The events do not allow for errors. Thus if the value can not be calculated then the pseudo attribute code should return a sensible default.