Today, I come back from the Tech Days in Antwerp and we see a very interesting thing.
A tool that can generate input data for your unit test (business). These input data are not random generated but are calculated to make your unit test to pass through all branches (if, else, catch, ...). The name of this great tool is "Plex", if you want to learn more about it, you can visit the research site : Pex site
A dataset is a class in .Net representing the structure similar of a SQL database. It contains one or more tables. You can create typed dataset, it's a class which inherits from the base class dataset and have tables with specified name, columns with specified names and types. It's very easy to create with Visual Studio, in the server explorer window when you are connected to a database, you simply create a new dataset and you drag and drop the tables you need. Next you run a query against a database or via a table adapter and you fill this dataset, it's very easy. A dataset implements all the interfaces for databinding such as IErrorDataInfo, INotifyPropertyChanged, ... (see Databinding and error validation in WinForm).
A custom object is a class that your write by your own. It contains properties (generally no business code) and basic validations (see Databinding and error validation in WinForm). You run a query against a database and you map SQL columns to the properties of your custom classes.
A dataset is very easy and is rapidly created but there are some problems for big projects :
Custom object doesn't have this problem :
For small projects dataset is a good choice, you can create rapidly an application with databinding. Pay attention that if you create a web service it's only for .Net clients.
For big projects dataset can lead to maintenance, evolution problems, it'll be difficult to change an existing dataset, the only solution will be to create a new one. With custom object we can make inheritance, create interfaces, ... to have a flexible design for future changes. It takes at the beginning a little more time to start the project in comparison with dataset because you need to create your objects and implements the necessary interfaces if you want to take advantages of databinding (see Databinding and error validation in WinForm). But now with linq and linq to SQL it's more easier to work with custom objects.
I write this post because I have searched a long time before to obtain an acceptable result with error validation and databinding.
With databinding and a little bit of code you can obtain the result from the screen shot rapidly and this code is very stable.
The first step is to write our business object, in this sample the class Person with 2 properties "Lastname" and "Firstname".
Next via the datasource window we drag and drop the first name and last name property into the window. The error property in the following screen shot will be explained later.
Next to show errors on our winform we add an error provider to the window and we can set the current error for each control via the validate event of each control but it's long and it's for each new form with the same object.
The error provider component have a property datasource, we can bind to it a dataset and it will show errors into data grid but for custom object?
You have to implement the interface IDataErrorInfo. This interface have 2 get properties Error and an indexer with a string as key. The error property return a message saying if the whole object have one or more errors, the indexer return for a property if the property is good or not. When a bound control lose focus, it will read the indexer property and the string parameter will be the property name to check, if we return a string different of null or empty, the property is in error state and the error provider will show it.
See the implementation of the Person class:
| 1 using System; 2 using System.Collections.Generic; 3 using System.Text; 4 using System.ComponentModel; 5 6 namespace DataBindingTest 7 { 8 class Person : IDataErrorInfo 9 { 10 private Dictionary<string, string> errors = new Dictionary<string, string>(); 11 12 private string error = string.Empty; 13 14 private string lastname; 15 private string firstname; 16 17 private void Validate(string field, string value) 18 { 19 switch (field) 20 { 21 case "Lastname": 22 if (String.IsNullOrEmpty(value)) 23 { 24 this.errors["Lastname"] = "There is an error"; 25 } 26 else 27 { 28 this.errors.Remove("Lastname"); 29 } 30 break; 31 case "Firstname": 32 if (String.IsNullOrEmpty(value)) 33 { 34 this.errors["Firstname"] = "There is an error"; 35 } 36 else 37 { 38 this.errors.Remove("Firstname"); 39 } 40 break; 41 default: 42 break; 43 } 44 } 45 46 public string Lastname 47 { 48 get 49 { 50 this.Validate("Lastname", this.lastname); 51 return this.lastname; 52 } 53 54 set 55 { 56 this.lastname = value; 57 this.Validate("Lastname", this.lastname); 58 } 59 } 60 61 public string Firstname 62 { 63 get 64 { 65 this.Validate("Firstname", this.firstname); 66 return this.firstname; 67 } 68 69 set 70 { 71 this.firstname = value; 72 this.Validate("Firstname", this.firstname); 73 } 74 } 75 76 #region IDataErrorInfo Members 77 78 public string Error 79 { 80 get 81 { 82 if (this.errors.Count > 0) 83 { 84 return "There are " + this.errors.Count + " errors"; 85 } 86 87 return null; 88 } 89 } 90 91 public string this[string columnName] 92 { 93 get 94 { 95 if (this.errors.ContainsKey(columnName)) 96 { 97 return this.errors[columnName]; 98 } 99 else 100 { 101 return null; 102 } 103 } 104 } 105 106 #endregion 107 } 108 } |
This method is good for basic validation such as null, length, regex validation.
Now if you change the property of our custom object via business code, it will not be reflected directly to the screen. The binding source doesn't know that the value has changed. The solution is to implement the interface INotifyPropertyChanged, it will declare the event PropertyChanged on your class. Then you raise this event giving to it the name of the property into the setter of all of the properties of the Person class and now the binding source will be notified of the change and refresh it on the screen.
| 61 public string Firstname 62 { 63 get 64 { 65 this.Validate("Firstname", this.firstname); 66 return this.firstname; 67 } 68 69 set 70 { 71 this.firstname = value; 72 if (this.PropertyChanged != null) 73 { 74 this.PropertyChanged(this, new PropertyChangedEventArgs("Firstname")); 75 } 76 this.Validate("Firstname", this.firstname); 77 } 78 } |
There are a lot of interfaces you can implement to have your live easier...
