Switch in View Computed column

 If you need to compare multiple fields in your view while populating a computed column, take into consideration that the standard implementation of method SysComputedColumn::switch uses a map enumerator. 

public static client server str switch(str _controlExpression, Map _comparisonExpressionMap, str _defaultExpression)
    {
        MapEnumerator  mapEnumerator;
        str caseExpression = '';

        caseExpression ='CASE ' + _controlExpression;
        mapEnumerator = _comparisonExpressionMap.getEnumerator();
        while (mapEnumerator.moveNext())
        {
            caseExpression += ' WHEN ' + mapEnumerator.currentKey() + ' THEN ' + mapEnumerator.currentValue();
        }
        caseExpression += ' ELSE ' + _defaultExpression;
        caseExpression += ' END';

        return caseExpression;
    }

It means that your given order will be replaced in final SQL clause by alphabetical one of your keys.

CASE  
	WHEN (T4.PROJID1) != ('') THEN T4.PROJNAME1 
	WHEN (T4.PROJID2) != ('') THEN T4.PROJNAME2 
	WHEN (T4.PROJID3) != ('') THEN T4.PROJNAME3 
	ELSE T4.PROJNAME END

For example, we want to populate field mgcProjInvoiceGLTransView.ParentProjectName for a given project id up to three level up in the project hierarchy. Let's assume that they are prepopulated in mgcProjInvoiceOnAccView view: projId1 is the parent of projId, projId2 is the parent of projId1, and so on.

Once we reference this computed column to the following method, we will get a new order in CASE construction on the SQL side.

 private static str projNameParent()
    {
        str         ret;
        SysComputedColumnBase::switch cannot keep a given order while using Map enumerator; so we put the SQL string as a string constant
        tableName   viewName                    = identifierStr(mgcProjInvoiceGLTransView);
        tableName   tableName                   = identifierStr(mgcProjInvoiceOnAccView);
        str         compareValue                = '';


        Map         comparisonExpressionMap     = SysComputedColumn::comparisionExpressionMap();
        str         fieldNameProjName3          = SysComputedColumn::returnField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjName3));
        str         fieldNameProjName2          = SysComputedColumn::returnField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjName2));
        str         fieldNameProjName1          = SysComputedColumn::returnField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjName1));
        str         fieldNameProjName           = SysComputedColumn::returnField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjName));

        comparisonExpressionMap.insert(
        SysComputedColumn::notEqualExpression(
            SysComputedColumn::comparisonField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjId3)),
            SysComputedColumn::comparisonLiteral(compareValue)),
        fieldNameProjName3);

        comparisonExpressionMap.insert(
        SysComputedColumn::notEqualExpression(
            SysComputedColumn::comparisonField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjId2)),
            SysComputedColumn::comparisonLiteral(compareValue)),
        fieldNameProjName2);

        comparisonExpressionMap.insert(
        SysComputedColumn::notEqualExpression(
            SysComputedColumn::comparisonField(viewName, tableName, fieldStr(mgcProjInvoiceOnAccView, ProjId1)),
            SysComputedColumn::comparisonLiteral(compareValue)),
        fieldNameProjName1);

        ret       = SysComputedColumn::switch(
                                                '',
                                                comparisonExpressionMap,
                                                fieldNameProjName);
        return ret;
    }

Of course, it always returns  the name of the parent on the first level, even though it had its own parent, which is incorrect result. 

Therefore, the easiest way is to replace the aforementioned construction with a simple string.

 private static str projNameParent()
    {
        str         ret;
        ret = "CASE WHEN (T4.PROJID3) != ('') THEN T4.PROJNAME3 WHEN (T4.PROJID2) != ('') THEN T4.PROJNAME2 WHEN (T4.PROJID1) != ('') THEN T4.PROJNAME1 ELSE T4.PROJNAME END";
        return ret;
    }