Sunday, September 28, 2008
Restricting Read/Write Access To Fields

Data Aquarium Framework provides multiple options to allow precise control of read and write access to data fields displayed in grid and form views.

Generate an Aquarium Express application with Code OnTime Generator and Northwind database. Open ~/Controllers/Products.xml and follow instructions to try various methods of restricting user's ability to change the UnitPrice field values.

ReadOnly Attribute

If you want to prevent your users from changing field values then defining readOnly attribute on fields in data controller will do the trick.

<field name="UnitPrice" type="Decimal" default="(0)" 
  label="Unit Price" readOnly="true"/>

This is how the field is rendered in the grid view of sample application when you try to edit any row.


Notice that readOnly attribute will affect all grid and form views in the data controller.

Duplicate Field With ReadOnly Attribute

Sometimes you may want to prevent users from editing field in a grid view but still want to allow editing in forms. A simple solution is to define an additional field in your SQL query with matching field element adorned with readOnly attribute.

Here is how you can change the query that retrieves Products. The query includes a duplicate field that selects UnitPrice with an alias UnitPriceReadOnly.

    "Products"."ProductID" "ProductID"
    ,"Products"."ProductName" "ProductName"
    ,"Products"."SupplierID" "SupplierID"
    ,"Supplier"."CompanyName" "SupplierCompanyName"
    ,"Products"."CategoryID" "CategoryID"
    ,"Category"."CategoryName" "CategoryCategoryName"
    ,"Products"."QuantityPerUnit" "QuantityPerUnit"
    ,"Products"."UnitPrice" "UnitPrice"
    ,"Products"."UnitPrice" "UnitPriceReadOnly"
    ,"Products"."UnitsInStock" "UnitsInStock"
    ,"Products"."UnitsOnOrder" "UnitsOnOrder"
    ,"Products"."ReorderLevel" "ReorderLevel"
    ,"Products"."Discontinued" "Discontinued"
from "dbo"."Products" "Products"
    left join "dbo"."Suppliers" "Supplier" 
      on "Products"."SupplierID" = "Supplier"."SupplierID"
    left join "dbo"."Categories" "Category" 
      on "Products"."CategoryID" = "Category"."CategoryID"

Add a matching field UnitPriceReadOnly to the fields section of the data controller.

<field name="UnitPriceReadOnly" type="Decimal" default="(0)" 
  label="Unit Price"  readOnly="true"/>

Next change the definition of grid1 view to prevent users from editing the field by replacing reference to UnitPrice with the reference to UnitPriceReadOnly.

<view id="grid1" type="Grid" commandId="command1" label="Products">
  <headerText>This is a list of products. </headerText>
    <dataField fieldName="ProductName" columns="40" />
    <dataField fieldName="SupplierID" aliasFieldName="SupplierCompanyName" />
    <dataField fieldName="CategoryID" aliasFieldName="CategoryCategoryName" />
    <dataField fieldName="QuantityPerUnit" columns="20" />
    <dataField fieldName="UnitPriceReadOnly" 
      dataFormatString="c" columns="15" />
    <dataField fieldName="UnitsInStock" columns="15" />
    <dataField fieldName="UnitsOnOrder" columns="15" />
    <dataField fieldName="ReorderLevel" columns="15" />
    <dataField fieldName="Discontinued" />

Form views editForm1 and createForm1 will retain references to the original field UnitPrice, which allows users to make price adjustments in form mode only.

WriteRoles Attribute

A superior approach is to rely on the security infrastructure of ASP.NET and its support in Data Aquarium Framework.

Attribute roles defined on a field will limit visibility of the field in views to users with the specified roles. Field writeRoles will prevent users from changing the field if the user's role is not on a comma-separated list.

If you add this attribute as shown in the snippet then the result will be a read-only display to all users that do not have Admin role.

<field name="UnitPrice" type="Decimal" default="(0)" 
  label="Unit Price" writeRoles="Admin"/>

The sample application generated with Aquarium Express project is relying on Windows authentication by default. Role Admin is not defined in a typical Windows configuraiton and this will cause the UnitPrice to be displayed as read-only in all grid and form views of Products data controller.

Most Windows user accounts belong to Users group. If you replace Admin with Users then an editable version of UnitPrice field is presented.

The same role level access is available if you switch your application to forms authentication or create a custom role and/or user manager.

You can read more about field-level security in Data Aquarium Framework applications in the post Using "roles" And "writeRoles" Attributes With Fields And Actions.