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Phase 2 / DisplayNameAttribute and DescriptionAttribute

DataField names are often shown in the user interface. For example, in a field's label, a column title, or a validation error message. The actual column name is often not user friendly and is certainly not localized.

DataFields can provide four different strings, localized if needed, when you use the DESDA.DisplayNameAttribute and DESDA.DescriptionAttribute.

The DESDA.DisplayNameAttribute provides most used value, called "DisplayName". It also offers a ShortDisplayName property where you can provide a smaller version of the text.

The DESDA.DescriptionAttribute provides text often used as a hint or tooltip called the "Description". It also provides the Prompt property for text to show in a prompt within the user interface.

Note Microsoft includes System.ComponentModel.DataAnnotations.DisplayAttribute which also has these values. It is supported by BLD. Its design is to include all kinds of properties that the user interface may use, including scaffolding and filtering. BLD prefers to assign each of these concepts to their own attributes and give them more features.

Here are some DESDA.DisplayNameAttribute and DESDA.DescriptionAttributes associated with the Product Entity class.

public class ProductMetadata
   [DESDA.DisplayName("Product ID", ShortDisplayName="ID")]
   public object ProductID { get; set; }

   [DESDA.DisplayName("Product Name", ShortDisplayName="Name")]
   [DESDA.Description("The product name.", Prompt="Enter the product name:")]
   public object ProductName { get; set; }
   [DESDA.DisplayName("Quantity Per Unit")]
   public object QuantityPerUnit { get; set; }

   [DESDA.DisplayName("Unit Price")]
   [DESDA.Description("The price of one unit", Prompt="Enter the price for one unit")]
   public object UnitPrice { get; set; }

The Source Code Browser shows completed DataAnnotations. The DESDA.DisplayNameAttribute and DESDA.DescriptionAttributes have been highlighted.

In the next topic, you'll learn how to supply defaults for DataFields when creating a new record.

Open the Source Code Browser (C# only)
Source Code Browser
/* ------------------------------------------------
 * Describes the Entity class for: Category
 * Classes:
 *    Category - Entity class. Edit it for validation and to customize metadata at runtime
 *    CategoryMetadata - Entity Metadata class. It contains the DataAnnotations.
 *    CategoryDAO - BLD DataAccessObject format version of a Data Access Object.

 * Requires .net 4.0 and these references:
 *    System.ComponentModel.DataAnnotations
 *    PeterBlum.DES
 *    PeterBlum.DES.DataAnnotations
 * Generated: 7/8/2011 4:17:08 PM
 * ------------------------------------------------*/
using System;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Collections.Generic;
using System.Linq;
using System.Data.Linq;
using PeterBlum.DES.DAO;
using PeterBlum.DES.DAO.Attributes;
using PeterBlum.DES.DAO.EntityDAO;
using PeterBlum.DES.DataAnnotations;

// Some members of this namespace have identical names to those in System.ComponentModel.DataAnnotations
// making it easy to switch from one to the other by adding the "DESDA." prefix
using DESDA = PeterBlum.DES.DataAnnotations;

namespace PeterBlum.WithDataAnnotations
   // --- ENTITY CLASS --------------------------------------------------
   /// <summary>
   /// Entity class. Edit it for validation and to customize metadata at runtime
   /// </summary>
   public partial class Category
/// <summary>
/// Associated with the CustomValidationAttribute on the Category.CategoryName property,
/// this uses LINQ to SQL to detect an existing Category with the same name
/// and reports it as an error.
/// </summary>
/// <remarks>
/// <para>You probably will create many of these methods. Consider using stored procedures
/// to search the database for duplicates. Write your code below to invoke the stored procedures.</para>
/// </remarks>
/// <param name="pNewName"></param>
/// <param name="pValidationContext"></param>
/// <returns></returns>
      public ValidationResult CheckForDuplicateCategoryNames(
         string pNewName, ValidationContext pValidationContext)
         BaseDAOChangeEntityActionArgs vArgs = (BaseDAOChangeEntityActionArgs)pValidationContext.GetChangeEntityActionArgs();

         ChangeEntityAction vAction = vArgs != null ? vArgs.Action : ChangeEntityAction.Update;
         if ((vAction == ChangeEntityAction.Insert) || (vAction == ChangeEntityAction.Update))
            Category vCategory = (Category)vArgs.Entity;
            int vThisCategoryID = (vAction == ChangeEntityAction.Insert) ? -1 : vCategory.CategoryID;
            NorthWindDataContext vDataContext = new NorthWindDataContext();
            System.Data.Linq.Table<Category> vTable = vDataContext.Categories;
            if (vTable.FirstOrDefault<Category>(category =>
               (String.Compare(category.CategoryName, pNewName, StringComparison.CurrentCultureIgnoreCase) == 0)
               && (category.CategoryID != vThisCategoryID)) != null)
               DESDA.EntityValidationResult vResult = new DESDA.EntityValidationResult(
                  "CheckForDuplicateCategoryNames", // this is the Source parameter. It can be anything. It is used by the BLDPageManager.UpdateErrorMessage event. So make it useful for detecting this particular error
                  "This name already exists. Choose another.",
                  typeof(Category), "CategoryName", pNewName);
               vResult.SummaryErrorMessage = "{LABEL} already exists. Choose another.";
               return vResult;

         return ValidationResult.Success;
   }  // class Category

   // --- ENTITY METADATA --------------------------------------------------
   /// <summary>
   /// Entity Metadata class.
   /// Companion to the Category Entity class that contains the DataAnnotations
   /// on properties with the same names as those in the actual Entity class.
   /// These properties do not require their types to match those in the Entity class.
   /// An Entity Metadata class allows the Entity class to be regenerated without
   /// overwriting DataAnnotations.
   /// </summary>
   [DESDA.InjectionSecurity(DetectScriptInjection=true, DetectSQLInjection=false)]  // impacts CategoryName, but not Description which has its own rules
   [DESDA.TableRestriction("Admin", DESDA.DenyAccess.None)]
   [DESDA.TableRestriction("Customer", DESDA.DenyAccess.Edit | DESDA.DenyAccess.Delete | DESDA.DenyAccess.Insert)]
   public class CategoryMetadata

      [DESDA.Filter(AutoGeneratePriority=DESDA.AutoGeneratePriority.Always, InMultiFieldSearch=true)]
      public object CategoryName { get; set; }
   /// <summary>
   /// In this example, explicitly make this a Multiline text element
   /// so it benefits from the MultilineText_Edit.ascx Field Template.
   /// Like most large textual fields, it should detect illegal hacking case.
   /// When the Peter's Input Security module is setup, the InjectionSecurityAttribute
   /// will block unwanted input.
   /// </summary>
      [DESDA.InjectionSecurity(DetectScriptInjection=true, DetectSQLInjection=true, 
      public object Description { get; set; }

      [DESDA.DbImageDataType(BadFormatErrorMessage="Bad format", ErrorMessage="Must be {EXTENSION}", SupportedFileTypes="jpg")]
      public object Picture { get; set; }

   }  // class CategoryMetadata

   // --- BLD DATAACCESSOBJECT  --------------------------------------------------
   /// <summary>
   /// BLD DataAccessObject class for the Category Entity class.
   /// It provides CRUD actions. The parent class already has default
   /// methods for Update(), Insert(), Delete() and several queries.
   /// </summary>
   /// <remarks>
   /// <para>For documentation, see the BLD DataAccessObject section of the Business Logic User's Guide.</para>
   /// </remarks>
   public class CategoryDAO : LINQtoSQLEntityDAO<Category>
      public CategoryDAO() : base(typeof(NorthWindDataContext)) { }
      public CategoryDAO(object pDataContext) : base(pDataContext) { }

   }  // class CategoryDAO