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Chapter 5. Using XML to Set Parameters
XML as a Way to Represent Hierarchies
AspGrid's object model has a hierarchical structure.
Writing ASP code for AspGrid is essentially
describing a hierarchy: we set
certain properties for the top-level object (Grid),
then for the second-level objects such as Table and Column,
then for the third-level objects (Cell, Header and Footer), etc.
There is a language (or strictly speaking, meta-language) that, among other
things, was designed to describe hierarchical information.
This language is, of course, XML (Extensible Markup Language).
Consider the following ASP code:
Grid.CanEdit = False
Grid.Cols(1).CanSort = True
Grid.Cols(1).Cell.BGColor = "#FF0000"
Grid.Cols(1).Cell.Font.Face = "Couirer"
Grid.Cols(1).Cell.Font.Size = "2"
Now, the same information XML-style (notice how child objects
are represented by nested XML tags):
<Grid CanEdit="False">
<Cols Index="1">
<CanSort>True</CanSort>
<Cell BGColor="#FF0000">
<Font Face="Courier" Size="2"/>
</Cell>
</Cols>
</Grid>
In case you have not mastered XML yet, here are a few important
things to know about an XML document:
- You can make up your own tags.
- Every opening tag requires a matching closing tag.
- If an element has no content (such as <FONT> is the above example), the opening and closing tags
may be combined into a single "shortcut" tag such as <TAG/>.
- XML is case-sensitive.
- The character " (double quote) in a string constant must
be denoted as ".
- An XML document may be subject to a
set of rules called "document type definition" (DTD). More about it later.
For more information on XML, visit the web site www.xml101.com.
Using XML with AspGrid
If you use XML to set AspGrid parameters, your ASP script can be reduced
to as little as 3 lines of code:
<%
Set Grid = Server.CreateObject("Persits.Grid")
Grid.LoadParameters "params.xml"
Grid.Display
%>
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The XML approach has the following advantages over the traditional script-based
approach:
- Cleaner, simpler code. Your AspGrid-related scripts will only contain 3 lines of code
instead of potentially dozens of lines.
- Reusability. You can place your favorite color/font scheme in an XML file
and re-use it from multiple ASP scripts.
- Simplified deployment and maintenance. Several
servers may share a single XML file. Changes in that file
will immediately propagate to all servers at once.
- More intuitive development.
Instead of VB script, you will be dealing with tags and attributes
which you may find more intuitive.
- Use an XML editor of your choice. You are no longer
tied to a development environment such as VID. Use any
XML editor you want.
ASP-XML "Rosetta Stone"
The Rosetta Stone is a stone slab on which parallel inscriptions
in Egyptian hieroglyphic, Greek and demotic characters
were found, making possible the decipherment of ancient hieroglyphics.
We will use the Rosetta Stone approach to demonstrate
the usage of XML for setting AspGrid parameters.
The table below presents the ASP code sample which we examined
in the previous chapter, and its XML equivalent, shown side by side. This XML document
used in this sample can be found
in the file \Samples\05_xml\employees.xml.
Click here to view it.
| ASP Code | XML |
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Set Grid = Server.CreateObject("Persits.Grid")
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<Grid>
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Grid.SQL = "select id, dept_id, name, salary,
hiredate, maritalstatus, fullyvested from employees"
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<SQL>select id, dept_id, name, salary,
hiredate, maritalstatus, fullyvested from employees</SQL>
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Grid("id").Hidden = True
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<Cols Index="id">
<Hidden>True</Hidden>
</Cols>
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Grid("dept_id").AttachForeignTable "select id, name from departments", 1, 2
Grid("dept_id").Caption = "Department"
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<Cols Index="dept_id">
<AttachForeignTable SQL="select id, name from departments" KeyCol="1" DispCol="2"/>
<Caption>Department</Caption>
</Cols>
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Grid("name").Caption = "Full Name"
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<Cols Index="name">
<Caption>Full Name</Caption>
</Cols>
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Grid("salary").Caption = "Salary"
Grid("salary").FormatNumeric 2, True, True, True, "$"
Grid("salary").Cell.Align = "RIGHT"
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<Cols Index="salary">
<FormatNumeric Decimal="2" Prefix="$"/>
<Caption>Salary</Caption>
<Cell Align="RIGHT"/>
</Cols>
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Grid("hiredate").FormatDate "%b %d, %Y" ' Mon DD, YYYY
Grid("hiredate").Caption = "Hire Date"
Grid("hiredate").DefaultValue = CDate("5/18/2000")
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<Cols Index="hiredate">
<FormatDate Format="%b %d, %Y"/>
<Caption>Hire Date</Caption>
<DefaultValue Type="date"> 05/18/2000</DefaultValue>
</Cols>
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Grid("maritalstatus").Array = Array("Single", "Married", "Divorced")
Grid("maritalstatus").VArray = Array(3, 2, 1)
Grid("maritalstatus").Caption = "Marital Sts"
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<Cols Index="maritalstatus">
<Array>
<Item Value="Single" DBValue="3"/>
<Item Value="Married" DBValue="2"/>
<Item Value="Divorced" DBValue="1"/>
</Array>
<Caption>Marital Sts</Caption>
</Cols>
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Grid("fullyvested").Caption = "Vested"
Grid("fullyvested").AttachCheckbox "Yes", "No"
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<Cols Index="fullyvested">
<AttachCheckbox Checked="Yes" Unchecked="No"/>
<Caption>Vested</Caption>
</Cols>
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Grid(0).Header.BGColor = "#B0B0FF"
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<Cols Index="0">
<Header BGColor="#B0B0FF"/>
</Cols>
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Grid(999).Header.BGColor = "#B0B0FF"
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<Cols Index="999">
<Header BGColor="#B0B0FF"/>
</Cols>
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Grid.ColRange(2, 7).CanSort = True
Grid.ColRange(2, 7).Header.BGColor = "#B0B0FF"
Grid.ColRange(2, 7).Header.Font.Face = "Arial Narrow"
Grid.ColRange(2, 7).Cell.Font.Face = "Arial Narrow"
Grid.ColRange(2, 7).InputSize = 10
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<ColRange From="2" To="7">
<CanSort>True</CanSort>
<Cell>
<Font Face="Arial Narrow"/>
</Cell>
<Header BGColor="#B0B0FF">
<Font Face="Arial Narrow"/>
</Header>
<InputSize>10</InputSize>
</ColRange>
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Grid.ImagePath = "../images/"
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<ImagePath>../images/</ImagePath>
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Grid.ShowLeftSideButtons
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<ShowLeftSideButtons/>
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Grid.Table.CellSpacing = 0
Grid.Table.CellPadding = 1
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<Table CellPadding="1" CellSpacing="0">
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Grid.Table.Caption = "Employees"
Grid.Table.Caption.Font.Face = "Arial"
Grid.Table.Caption.Font.Bold = True
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<TableCaption Value="Employees">
<Font Face="Arial" Bold="True"/>
</TableCaption>
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</Table>
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Set Grid = Nothing
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</Grid>
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Here is what the file http://localhost/aspgrid/Samples/05_xml/employees_xml.asp
looks like:
<%
' Build connection string to aspgrid.mdb
strConnect = "DRIVER={Microsoft Access Driver (*.mdb)};DBQ=" &_
Server.MapPath("..\db\aspgrid.mdb")
' Create instance 2 of AspGrid for the Employees table
Set Grid = Server.CreateObject("Persits.Grid")
' Connect
Grid.Connect strConnect, "", ""
' Load parameters from XML file
Grid.LoadParameters Server.MapPath("employees.xml")
' Display grid
Grid.Display
Grid.Disconnect
%>
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There is a few things worth noting:
- Not every AspGrid expression has an XML equivalent.
Methods and properties such as
Grid.Display, Grid.BuildForm, Grid.Disconnect, Grid.Connection and Grid.Recordset
must be explicitly called by ASP script.
- Dynamic expressions also need to be specified by ASP code
and not XML. In our code sample we call the Connect method explicitly
because one of its arguments is computed dynamically.
- The LoadParameters method can be called multiple
times on different XML files within the same ASP script.
Playing by the Rules - the DTD
The sample XML file employees.xml starts with the following two lines:
<?xml version="1.0"?>
<!DOCTYPE Grid SYSTEM "AspGrid.dtd">
The first line identifies the version
of the XML specification to which this document conforms.
The second
line points to a file that contains the Document Type Definition (DTD)
for this XML document. Essentially, this line
says: "I am an XML document that conforms to the rules set forth
in the file AspGrid.dtd."
What rules are those? The DTD describes
what the root element of the XML document should be (<Grid> in our case),
what attributes are allowed for this element, and among those, which
are required and which are optional. Also it describes
the sub-elements for the root element, in what order they must appear,
and, of course, their own attributes and sub-elements.
When are these rules enforced, and by whom? AspGrid internally
uses the Microsoft XML processor, msxml.dll, that comes with IE 5.0.
When your script calls LoadParameters, this method passes the specified
XML document to msxml. The XML processor then parses the document
and compares it against the file AspGrid.dtd to see if all the rules
are conformed to. If not, an error will be thrown similar to this:
Persits.Grid.1 (0x800A002C)
XML Parse Error: Element content is invalid according to the DTD/Schema. Expecting: Cols, ColRange, DeleteButtonOnClick, ExtraFormItems, FileName, FormOnSubmit, ImagePath, SaveButtonOnClick, SQLAfterDelete, SQLAfterInsert, SQLAfterUpdate, SQLBeforeDelete, SQLBeforeInsert, SQLBeforeUpdate, ShowLeftSideButtons, Table. Source: file:///D:/MyProjects/AspGrid3/samples/05_xml/employees.xml. Line 8
This is what the beginning of the AspGrid.dtd file looks like:
<!ELEMENT Grid (Connect?, SQL?, Cols*, ColRange*,
DeleteButtonOnClick?, ExtraFormItems?, FileName?,
FormOnSubmit?, ImagePath?, SaveButtonOnClick?,
SQLAfterDelete?, SQLAfterInsert?, SQLAfterUpdate?,
SQLBeforeDelete?, SQLBeforeInsert?, SQLBeforeUpdate?,
ShowLeftSideButtons?, Table?)>
<!ATTLIST Grid CanAppend CDATA #IMPLIED>
<!ATTLIST Grid CanDelete CDATA #IMPLIED>
<!ATTLIST Grid CanEdit CDATA #IMPLIED>
<!ATTLIST Grid MaxRows CDATA #IMPLIED>
<!ATTLIST Grid MethodGet CDATA #IMPLIED>
<!ATTLIST Grid NumberOnPage CDATA #IMPLIED>
<!ATTLIST Grid ReadOnly CDATA #IMPLIED>
<!ATTLIST Grid ShowHeader CDATA #IMPLIED>
<!ATTLIST Grid UseImageButtons CDATA #IMPLIED>
This portion of the DTD file states that the root element of
our XML file (<Grid>) accepts the following optional attributes: CanAppend, CanDelete,
CanEdit, MaxRows, etc. It also says that the Grid element
accepts the following sub-elements: <Connect>, <SQL>,
<Cols>, <ColRange>, etc (in this order). The ?
sign indicates that the element can appear 0 or 1 times.
The * (asterisk) sign means the element can appear 0 or more times.
The rest of the DTD describes each individual sub-element (its own
arguments and sub-elements).
The Microsoft XML processor is very strict about the order in which
sub-elements appear within an element. For example, <Table>
may not appear before, say, <SQL> within <Grid>
When designing your XML document, always consult the AspGrid.dtd file.
Click here to view the file AspGrid.dtd.
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