I am a beginner when it comes to databases and c# (using them together) and I am trying to associate the values from a database to the attributes of a class.
I remember seing somewhere something like:
private attribute
[Data binding]
public Attribute
{
get { return attribute; }
set { attribute = value; }
}
What is it? What should I look to use something like this. I am using an ADO.NET EMD, but I'm not sure what to do next mainly because I am not sure what to look into.
You're probably thinking of the [Bindable] attribute that can be placed on properties of a Control to tell Visual Studio to show the property in the DataBindings node in the designer.
It's expected that you'll wire up that attribute to something in your UserControl, like a textbox.
Related
In an old WPF project I have a class with Properties like this:
private string _name = "";
public string Name
{
get { return _name; }
set
{
string cleanName = clsStringManip.CleanText(value, true);
if (cleanName != _name)
{
_name = cleanName;
}
}
}
Where every time the name changes, I ensure that the value is "cleaned". Putting it in the property ensures I never forget to clean the string before setting the property on the object.
Now I am recreating this system using MVC5 and EntityFramework6.1 using DatabaseFirst.
So all the properties are autogenerated by EF. How then can I add the equivalent CleanText function to my properties without editing the autogen code? - as I'll lose these changes next time I change my database and resync.
All I can find via Google is a way add data annotations via MetadataType and partial classes but this doesn't answer my question.
I tried to add the above code into a partial class but get the error:
The type XXX already contains a definition for Name
The only way I can think is to create a bunch of SetProperty() functions but this is dirty and you can never ensure other developers (or myself) will remember to use them.
Disclaimer: I haven't used EF 6 yet.
Let me answer this in two parts. First, I will tell you how to do this. Then I will tell you why I don't think you should do this. :-)
HOW:
As you discovered, you cannot create another Name property. You need to modify the way the EF generates the code, so that it gives you a place to insert your new code. Depending on how you are using the EF, it often generates Validate() method calls or OnPropertyChanged() calls. You may be able to do what you want inside of those methods.
If you can't do this in Validate() or OnPropertyChanged(), you could change the T4 template to generate something like this:
private string _name = "";
public string Name
{
get { return _name; }
set
{
string cleanName = value;
Cleanup_Name(ref cleanName);
if (cleanName != _name)
{
_name = cleanName;
}
}
}
private partial void Cleanup_Name(ref string);
This gives you a partial method that you can then implement as you see fit. So for any property you want to customize, you can now add another file to your project that does this:
public partial class MyEntity {
void Cleanup_Name(ref string name)
{
// Put your logic in here to fixup the name
}
}
If you do not write the above code block, then the partial method is simply a no-op. (Partial methods must return void, hence the use of a ref parameter).
WHY NOT?
The advantage of this method is that it is totally transparent to the developer. The property is just magically changed. But there are several disadvantages:
Some controls expect that if they call name = "123" that if they get the name back, it is "123" and will fail if this happens. Values are changing but no PropertyChanged event fired. If you do fire the PropertyChanged, then they sometimes change the value back. This can cause infinite loops.
There is no feedback to the user. They typed in one thing, and it looked right, but now it says something different. Some controls might show the change and others won't.
There is no feedback to the developer. The watch window will seemingly change values. And it is not obvious where to see the validation rules.
The entity-framework itself uses these methods when it loads data from the database. So if the database already contains values that don't match the cleanup rules, it will clean them when loading from the database. This can make LINQ queries misbehave depending on what logic is run on the SQL server and what logic is run in the C# code. The SQL code will see one value, the C# will see another.
You might also want to look into what the Entity-Framework's change tracking does in this case. If a property set does a cleanup while loading values from the database, does it consider that a change to the entity? Will a .Save() call write it back to the database? Could this cause code that never intended to change the database to suddenly do so?
ALTERNATIVE
Instead of doing this, I suggest creating a Validate() method that looks at each property and returns errors indicating what is wrong. You could also even create a Cleanup() method that fixes the things that are wrong. This means the cleanups are no longer transparent, so the developer must call them explicitly. But that is a good thing: the code isn't changing values without them realizing it. The person writing the business logic or the UI knows at what point the values will change, and can get a list of why.
The only way you can achieve this is by creating a new property you actually use in your application. Perhaps you can hide the original property in the designer. The actual property you use could look like this:
public string ExternalName
{
get { return Name; }
set
{
string cleanName = clsStringManip.CleanText(value, true);
if (cleanName != Name)
{
Name = cleanName;
}
}
}
As an alternative, you can use POCO classes:
If you want to keep using database-first, check this answer
Use code-first for an existing database, see this detailed guide
Add partial to the generated class.
Change the scope of Name in the generated class from public to internal.
Add the following in the same assembly:
public partial class classname
{
[NotMapped]
public string CleanName
{
get { return Name; }
set
{
var cleanName = clsStringManip.CleanText(value, true);
if (cleanName != Name)
Name = cleanName;
}
}
}
Caveat: you'd have to remember to do steps 1-2 every time you regenerated your POCOs ... I'd seriously consider Code First to Existing Database.
EDIT
Optionally:
Rename Name as InternalName in the generated classname; decorate it with [Column("Name")].
Rename CleanName as Name in the partial class under your control.
Caveat in 4 becomes "remember to do steps 1, 2, and 5 every time you regenerate POCOs".
This approach has the added benefit of not having to modify any of your client code (i.e., use of Name remains Name). And I'd still strongly consider Code First to Existing Database.
I have to make many combination of field and property. I cannot use the implicit property version "{ get; set; }" since the fields need some attributes.
So, in Visual Studio Express 2013, is there a way to have a shortcut to create a property associated with a field I just ended up writing?
Let's say I write;
private MyType myData;
and I press CTRL+P (whatever the shortcut), and it adds
public MyType MyData
{
get { return myData; }
set { myData = value; }
}
just after.
Is it possible?
EDIT:
The Express version however does only have two refactoring functionalities: rename and extract method, the other functionalities like encapsulate are not present.
I guess I'm stuck.
By what you are asking 3 simple clicks will do it like this:
rigth-click in your field then Refactor-->EncapsulateField
And your done.
Check this out:
http://msdn.microsoft.com/en-us/library/z41h7fat.aspx
this might also be useful (Create your own snippets) :
http://msdn.microsoft.com/en-us/library/vstudio/ms165394.aspx
here you have all the code snippets you need including "prop", which is the one you need now!
Hope it helps
Type prop
then press tab
then enter the property name
then press ctrl+.
then click on convert to full property
You should use code snippet and assign hotkey for it.
More information about managing code snippets here: http://msdn.microsoft.com/en-us/library/ms165394.aspx
I have this class:
public class MyProps
{
public MyProps()
{
}
protected string myVar;
public string MyProperty
{
get { return myVar; }
set { myVar = value; }
}
protected int myOtherVar;
public int MyOtherProperty
{
get { return myOtherVar; }
set { myOtherVar = value; }
}
}
That I want to add to my Form, so when I inherit from it I will be able to fill the properties in the MyPropsX property.
I have this code in my form:
protected MyProps propsX = new MyProps();
[TypeConverter(typeof(ExpandableObjectConverter))]
public MyProps MyPropsX
{
get
{
return propsX;
}
set
{
propsX = value;
}
}
Now, the properties MyProperty and MyOtherProperty are nicely shown in the Properties Window, and I can set their values directly there.
But when I close my form and I open it again, all my changes are lost, the properties being reset to show zero and an empty string.
What am I missing?
Should I inherit my MyProps class from certain special class or interfase?
Or some special attribute?
This is a little bit much for a comment and maybe your solution, so i'm answering to your comment with an answer instead with another comment:
With does not happen when I put properties directly on a form you mean, you are using the designer to set some property of the form. These will be written into the MyForm.designer.cs file. When you go into the code of your class you'll find within the constructor a method InitializeComponent(). Set the cursor on it an press F12. Here you can see what the designer has written into all the properties. You should respect the comment above the mentioned method and not start to modify the code with the code editor unless you really have understand how and when the designer will read and write code here (which is another chapter i can explain if needed). Otherwise it will happen that trying to opening your form with the designer after the code change will lead to an error message or code loss.
If you like to set some default value also, you should go back into the constructor and add the needed initialization code below the InitializeComponent() function and everything should work as expected.
Update
As you wrote in your comment you already know how the Designer interacts with the *.designer.cs file. So i really can't understand your concrete problem but maybe one of these articles can give you a more insight about how Microsoft wrote their components:
Make Your Components Really RAD with Visual Studio .NET Property Browser
Components in Visual Studio
This is very normal, since each time you are closing the form and opening it again you are having a new instance from the form MyPropsX, so the best way would be to save your properties in any kind of a database (sql, access, textfiles,...)
According to Microsoft:
http://msdn.microsoft.com/de-de/library/system.data.linq.mapping.columnattribute.expression.aspx
It's possible to add expression to the Linq-to-SQL Mapping.
But how to configure or add them in Visual Studio in the Designer?
Problem, when I add it manual to thex XYZ.designer.cs it on change it will be lost.
//------------------------------------------------------------------------------
// <auto-generated>
// This code was generated by a tool.
// Runtime Version:2.0.50727.4927
//
// Changes to this file may cause incorrect behavior and will be lost if
// the code is regenerated.
// </auto-generated>
//------------------------------------------------------------------------------
This is generated:
[Column(Name="id", Storage="_id", DbType="Int")]
public System.Nullable<int> id
{
...
But i need something like this
[Column(Name="id", Storage="_id", DbType="Int", Expression="Max(id)")]
public System.Nullable<int> id
{
...
Thanks.
According to this article:
http://msdn.microsoft.com/en-us/library/system.data.linq.mapping.columnattribute.expression.aspx
you should use the ColumnAttribute.Expression Property when you use CreateDatabase to define a column as containing computed values.
So you should check this article:
http://msdn.microsoft.com/en-us/library/Bb399420%28v=VS.100%29.aspx
Another way is to define expression on your sql server so it'll be mapped by the LINQ designer.
Edit: mmmm you edited your question, so probably my answer is not gonna help you so much, but you might be able to do this anyway with your 'extended' question :D
I do this by adding another class file to the project, give them the same name as the object from LinQ-to-SQL you want to extend and define it as partial.
for example, if you have a table called Files, the object File will be created for you by L2S. If you then create a file (with the same namespace as your DataContext object), and make it partial, like this:
public partial class File
{
}
You can just add properties, methods, etc. From within this class, you also have direct access to the properties of the 'other' File class.
It's a little klugy, but in your linq2sql designer, rename the field from 'id' to 'xid' (or anything else) and change its accessibility to internal.
then, in another file, start another partial class, like Wim Haanstra showed, and create a new property called 'id', add all the attributes you want, and in the get & set, just map it to and from the original property, now called 'xid'.
it would look something like this:
public partial class File
{
public int? id
{
get { return xid; }
set { xid = value; }
}
}
this is more commonly done to map fields in the database to a different type in the object, e.g. an int in the DB to an enum in the object, a byte/smallint/etc. in the DB, a boolean in the object. or to add attributes, like [DataMember] to the property.
I got below code from http://msdn.microsoft.com/en-us/library/dd584174(office.11).aspx for adding custom property in webpart tool pane. What does square bracket ([]) mean in the below code?
[Category("Custom Properties")]
[WebPartStorage(Storage.Personal)]
[FriendlyNameAttribute("Custom Color")]
[Description("Select a color from the dropdown list.")]
[Browsable(true)]
[XmlElement(typeof(System.Drawing.KnownColor))]
public System.Drawing.KnownColor MyColor
{
get
{
return _myColor;
}
set
{
_myColor = value;
}
}
As #Spencer Ruport said, they're attributes. They're used within .NET for declarative programming.
You can find information on each of these attributes at MSDN. However, you should know that the name of the attribute can be shortened. In your case, for example, Category is the short form of the class name CategoryAttribute and XmlElement is the short form of the class name XmlElementAttribute. When declaring attributes, the Attribute portion of the class name can be left out.
I've used most of these attributes in conjunction with the PropertyGrid control (see here for an example), although in your case, they are used for a Web Part property pane. The purpose is still the same. The attributes are used by the control to know how to display the property to the user. By using a combination of the various attributes that the control understands, it is possible to declaratively dictate this behavior.
I hope that helps a little bit, but Spencer is correct, you'll learn a lot more reading about attributes via Google than I can explain here.
They're called attributes.
Here's a quick example of how they can be used: http://www.codeproject.com/KB/cs/attributes.aspx