Tag: C#

Error intercepting in MVC when saving data

I have seen many times in MVC the following code , when doing a post and saving data :

try
{
        //code to save to database
}
catch
{
         ModelState.AddRuleViolations(TheModel.GetRuleViolations());
}

Why is not good ?
I will do a simple example : if some error occurs on the database level ( such as simple unique index on a name column ) or even some error occurs whenestablishing the database connection – you will never see what’s happening. And you will have no chance to repair the problem
A slighty better code is :

try
{
     ModelState.AddRuleViolations(TheModel.GetRuleViolations());
     if(ModelState.Count == 0)// no error in the model
     {
     //code to save to database
     }
}
catch(Exception ex)
{
      ModelState.AddModelError("", ex.Message);
}

Please see also how to do logging to the exception at
http://msprogrammer.serviciipeweb.ro/2010/04/19/logging-and-instrumentation/

Find the Error

This code was written by me, in a late night moment, when copy paste seems the best option
It started this way :

public string ImportFeed(string URL)
        {
            string ret = "";
            XmlDocument xd = new XmlDocument();
            xd.Load(URL);            
            for(int i=0;i<xd.ChildNodes.Count;i++)
            {
                ret += xd.ChildNodes[i].Name;
            }
            return ret;
             
        }

So far , nothing special. Just open the url, read into an XML , return first nodes. Then I wanted more – next nodes. Nothing easier – why bother with recursion or proper variable names ? Just copy and paste :

public string ImportFeed(string URL)
        {
            string ret = "";
            XmlDocument xd = new XmlDocument();
            xd.Load(URL);            
            for(int i=0;i<xd.ChildNodes.Count;i++)
            {
                ret += xd.ChildNodes[i].Name;
                for (int j = 0; i < xd.ChildNodes[i].ChildNodes.Count; j++)
                {
                    ret += xd.ChildNodes[i].ChildNodes[j].Name;
                }
            }
            return ret;
             
        }

Could you spot the error ?
Hint : I have discovered after 10 seconds …but not looking at the code…

C# quiz

Fast small quiz for sunny afternoon :
What is writing at the console those lines : ( please do not use a compiler) :

decimal? v = 100;
Console.WriteLine(v);
decimal? x = null;
x += v.Value;
Console.WriteLine(x);

ASP.NET MVC editing fast a property

There are some moments when you want to fast edit a property ( like a status or a name) and you do not want to load the entire “Edit” form for this.More, you are in an edit formula and do not want to add a form.

So here is the solution in ASP.NET MVC with jquery-1.4.2.min , jquery-ui-1.8.1.custom.min for a modal dialog and some controllers. The most difficult were the javascript, so I let to the final.

We will be editing the name for an employee in 4 steps.The most difficult to understand is the step 4(javascript) , however, it can be re-used with any other object- so you can put it in a common js file.

Step 1

create a view for editing the name , named FastEditEmp

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<BusinessLogic.Employee>" %>
<!-- edit inline the name -->
<%= Html.HiddenFor(Model=>Model.ID) %>
<%= Html.LabelFor(model=>model.Name) %>
<%= Html.EditorFor(model=>model.Name) %>

Step 2

Create the controllers and verify it works – at least the get action .

public ActionResult FastEditEmp(int id)
 {
 var emp=EmployeeList.LoadFromID(id);
 return View(emp);
 }
 [HttpPost]
 public ActionResult FastEditEmp(BusinessLogic.Employee emp)
 {
 try
 {
 
 var dbid = EmployeeList.LoadFromID(emp.ID);
 UpdateModel(dbid);
 dbid.Save();
 return new JsonResult() { Data = new { ok = true, message = "succes" } };
 
 }
 catch (Exception ex)
 {
 //TODO : log
 return new JsonResult() { Data = new { ok = false, message = "error : " + ex.Message } };
 
 }
 }

Step 3
Create the hyperlink to edit the name of an employee (emp) :

Step 4

This is the most difficult one, the javascript. However, more of the code is common no matter what you want to edit fast modal :

var wait = '<%= ResolveUrl("~/Content/Images/wait.gif") %>';
function EditModal(empID,url)
{
// load a please wait dialog
 var $dialog1 = $('<div></div>')
 .html("Loading data <br /> <img src='" + wait + "'></img>")
 .dialog({ autoOpen: false,
 title: 'please wait'
 });
 $dialog1.dialog('open');
// so the please wait dialog was shown to the user. Now load the content of the action specified in url
 $.get(url,
 {
 ID: empID
 },
 function(txt) {
 
 var $dialog = $('#dialog');
 $dialog.html('');
 $dialog.html(txt)
 .dialog({
 autoOpen: false,
 title: 'Edit',
 modal: true,
 show: 'blind',
 hide: 'explode',
 closeOnEscape: false,
 buttons: {
 
 "Close": function() {
//just cleanup - no saving
 var allInputs = $(":input:not(:button)");
 var ser = allInputs.serialize();
 allInputs.remove();
 allInputs.empty();
 $(this).dialog("close");
 $(this).dialog('destroy');
 
 },
 "Save": function() {
//now saving data : serializing and posting
 var allInputs = $(":input:not(:button)");
 var ser = allInputs.serialize();
 allInputs.remove();
 allInputs.empty();
 
 window.alert(ser); -- debug mode
 $(this).dialog('close');
 $(this).dialog('destroy');
//saving data by posting to same url!
 $.post(url,
 ser,
 function(text) {
 $(this).dialog("close");
 $(this).dialog('destroy');
 if (text.ok) {
 
 window.alert("Saved - you can change here the display id with jquery");
 window.location.reload(true);
 }
 else {
 window.alert(text.message);
 }
 
 }
 );
 
 }
 
 }
 
 });
 
 $dialog1.dialog('close');//closing the wait dialog
 $dialog.dialog('open'); // show main editing dialog
 });
 
}
 
 </script>

As always, please find here the saving modal files. Please execute first the emp.sql file, then modify the connection string into the web.config .

Asp.NET MVC and DOS – re-using the ViewModels

(Please read first : http://msprogrammer.serviciipeweb.ro/2010/03/29/asp-net-mvc-orm-and-viewmodels/ )

One of the biggest challenges in programming was write once- GUI everywhere ( Ok, ORM impedance mismatch is another story)

I mean by that re-using the logic from an application in another application. ASP.NET MVC , with the commitment to strongly viewmodels, make me think that it will be now easier to transfer the viewmodels to an console application.

Let’s see the usual Employee-Department and creation.

First the Database :

Then the ViewModel for creating an employeeand for list of employees

public class ViewModelEmployee
 {
 public static DepartmentList ListOfDepartments
 {
 get
 {
 //TODO : put this into cache to not load every time
 DepartmentList dl = new DepartmentList();
 dl.Load();
 return dl;
 }
 }
 }
 public class ViewModelEmployeeCreate : ViewModelEmployee
 {
 public Employee emp = new Employee();
 
 public static void SaveNew(Employee emp)
 {
 emp.SaveNew();
 }
 }
 public class ViewModelEmployeeList : ViewModelEmployee
 {
 public EmployeeList employees;
 public void Load()
 {
 employees = new EmployeeList();
 employees.Load();
 }
 }

And now the magic :

ASP.NET MVC DOS

[HttpPost]
 public ActionResult Create(Employee emp,long DepartmentID)
 {
 try
 {
 
 emp.Department = new Department() { ID = DepartmentID };
 ViewModelEmployeeCreate.SaveNew(emp);
 
 return RedirectToAction("Index");
 }
 catch(Exception ex)
 {
 ModelState.AddModelError("", ex.Message);
 return View(new ViewModelEmployeeCreate(){emp=emp});
 }
 }

Console.WriteLine("choose department");
 var listdep=ViewModelEmployee.ListOfDepartments;
 foreach (var item in listdep)
 {
 Console.WriteLine(item.ID + ")" + item.Name);
 
 }
 string s=Console.ReadLine();
 long DepartmentID;
 if (!long.TryParse(s, out DepartmentID))
 {
 Console.WriteLine("exit : not a long :" + s);
 return;
 }
 if (!listdep.Exists(item => item.ID == DepartmentID))
 {
 Console.WriteLine("not a valid id:" + s);
 return;
 }
 Employee emp = new Employee();
 emp.Department = new Department() { ID = DepartmentID };
 Console.Write("employee name ?");
 emp.Name= Console.ReadLine();
 ViewModelEmployeeCreate.SaveNew(emp);

Now for listing employees:

ASP.NET MVC DOS

public ActionResult Index()
        {
            ViewModelEmployeeList vmel = new ViewModelEmployeeList();
            vmel.Load();
            return View(vmel);
        }

ViewModelEmployeeList vmel = new ViewModelEmployeeList();
          vmel.Load();
          foreach (var item in vmel.employees)
          {
              Console.WriteLine(item.Name);
          }

As you can see , the codes are really similar ( although the console application is filled with first verification and the MVC is not )

Please download the application from testaddropdownlist

To install : run the emp.sql file, change in the app.config/web.config the connection string to point to the real database/sql server.

Summary : This simple application shows how to re-use ViewModels from an ASP.NET MVC and a DOS Console Application

Homework : Add WindowsForms application and do the same.

July 5, 2010
4 Comments
Andrei Ignat
ASP.NET MVC, DOS, Entity Framework, HowTo

EF , automatic history of table and T4 files (TT files)

Usually the data of the tables should be tracking for who modified it.

Think about inserting/updating/deleting an employee : you must know who did those actions and when. So you create another table, identically as structure, and you add another 3 fields , such as [ModifiedDate](when), [ModifiedBy](who), [ModifiedType] (what : insert, update, delete).

There are several methods to do it :

from database :
- you can use triggers and insert data into new table
- in Sql 2008 , you can use Change Data Capture ( see also http://cdchelper.codeplex.com/ for a GUI )
from programming code – every time you modify an object, you remember to modify the history object with appropiate data.

The drawback with the database approach is that you can not retrieve who done the modifications ( usually the applications connect under a single account and have a roles table)

The drawback with the programming approach is that the programmer must REMEMBER doing so…If he does not(and does not wrote tests for history), you are stuck…

In the following I propose an automatically history – that maps convention over configuration in my template, but it is easy for you to modify.

The solution works with Entity Framework 4.0 and, for more easily spearation of concerns , with POCO generators.

Let’s say you have the following tables :

As you see we have a Employee and a employee_history, an Department and Department_history

The conventions are:

the history table name = “object” table name + “_history” suffix

the history table fields = “object” table name fields +[ModifiedDate], [ModifiedBy], [ModifiedType]

(if you change those conventions , please change the modelhistory.tt file)

If you want to see in action , please download code history and do the following
1. create database tests
2. run history.sql
3. run project
4. if necessay, re-create the model1.edmx with the same name and replace the console application app.config with the new connection string

After works, please add any fields to department table and to department_history table(same field names/type) . Re-compile the application and modify the new field in department. You will see the modifications in the department_history table.

Ok,now how we do the magic :

We create two new tt file that points to the model.edmx .

The first one ModelHistory.tt , takes care of creating the constructor for history entities by taking a parameter from the original entity :

public Department_History(Department original):this()
{
this.IDDepartment=original.IDDepartment;
this.Name=original.Name;
}

How it do this magic ? Simple : the ModelHistory.tt recognize the model and history in the name of tables:

</pre>
string inputFile = @"Model1.edmx";
string History = "_History";
<pre>

then it generate code for constructor :

    #>
        public <#=code.Escape(entity)#>():base()
        {
        }
        public <#=code.Escape(entity)#>(<#=NameEntityOriginal #> original):this()
        {
        <#
    foreach (EdmProperty edmProperty in entityOriginal.Properties.Where(p => p.TypeUsage.EdmType is PrimitiveType && p.DeclaringType == entityOriginal))
    {
        #>
                this.<#= code.Escape(edmProperty.Name) #>=original.<#= code.Escape(edmProperty.Name) #>;
        <#
 
    }
    #>
        }
    <#
</pre>

Ok, and then how to create the history entity ? I wish that the POCO template has had an event “Database saving” – but the only thing I can have is SaveChanges from the ObjectContext – so I create a new ObjectContext , derived from the default one that comes with the project, and creates a new history object :

public override int SaveChanges(SaveOptions options)
{
this.DetectChanges();
DateTime dtModified=DateTime.Now;
string UserModified=clsUser.UserName;
foreach (ObjectStateEntry ose in this.ObjectStateManager.GetObjectStateEntries(EntityState.Added | EntityState.Deleted | EntityState.Modified))
{
 
//could do this way too
//if (ose.Entity != null && ose.Entity.GetType() == typeof(...))
//{
//}
if (ose.Entity != null)
{
string NameType=ose.EntitySet.ElementType.Name;
 
switch(NameType)
{
 
case "Department":
var itemDepartment_History = new Department_History(ose.Entity as Department);
//if compile error here, that means you keep tracking
//of which modified with another properties
//please modify the tt accordingly
itemDepartment_History.ModifiedType= ose.State.ToString();
itemDepartment_History.ModifiedDate= dtModified;
itemDepartment_History.ModifiedBy= UserModified;
base.Department_History.AddObject(itemDepartment_History);
break;
 
case "Employee":
var itemEmployee_History = new Employee_History(ose.Entity as Employee);
//if compile error here, that means you keep tracking
//of which modified with another properties
//please modify the tt accordingly
itemEmployee_History.ModifiedType= ose.State.ToString();
itemEmployee_History.ModifiedDate= dtModified;
itemEmployee_History.ModifiedBy= UserModified;
base.Employee_History.AddObject(itemEmployee_History);
break;
 
}
}
}
 
return base.SaveChanges(options);
}

Now all is ready and I made a console application for testing manually (ok, should make a NUnit / MSTest / xUnit )

using (var ctx = new testsEntitiesHistory())
           {
               var dep = new Department();
               dep.Name = "IT";
               ctx.Departments.AddObject(dep);
               ctx.SaveChanges();
               id = dep.IDDepartment;
           }
           using (var ctx = new testsEntitiesHistory())
           {
               var dep = ctx.Departments.Where(depart => depart.IDDepartment == id).FirstOrDefault();
               dep.Name = "Information tehnology";
               ctx.SaveChanges();
               //
           }
           using (var ctx = new testsEntitiesHistory())
           {
               var dep = ctx.Departments.Where(depart => depart.IDDepartment == id).FirstOrDefault();
               ctx.Departments.DeleteObject(dep);
               ctx.SaveChanges();
 
           }
           using (var ctx = new testsEntitiesHistory())
           {
               foreach (var dephist in ctx.Department_History)
               {
                   Console.WriteLine("Found {0} with state {1}", dephist.Name,dephist.ModifiedType);
               }
           }

And the output is :

history saving — automatically saving history department

Now you can add more tables to the edmx or change the fields – all is done automatically when compiling

If you want to see in action , please download code history

Update : for another way to do it( generating trigger and tables ) please see : http://msprogrammer.serviciipeweb.ro/2010/09/27/generating-history-trigger-with-ef-edmx-and-tt-files/

file helpers

More than one time you need to let users / application import bulk data in your system .

I have had many cases – data is old data from old software, that is exported in some text files, usually csv.

In order to import fast the data, I used FileHelpers from http://www.filehelpers.com/

Let’s say you have the following data for an car evidence :

Date, StartMiles, Destination, EndMiles

And the data comes from an Excel that has those columns. The requirements is the user can copy/paste from Excel data

When they copy the data comes in this form

01/01/2010 1000 Washington 1550

02/01/2010 1550 Dallas 2550

and so on.

It is clear that you :

have a class with Date, StartMiles, Destination, EndMiles
accomodate for space – but how to perform various data separator ( we suppose that first is the day, then comes the month).

Now the code in logical steps :

1. Accomodate for dates :

internal class ConvertDate : ConverterBase
{
 
        /// <summary>
        /// different forms for date separator : . or / or space
        /// </summary>
        /// <param name="from">the string format of date - first the day</param>
        /// <returns></returns>
 
        public override object StringToField(string from)
        {
            DateTime dt;
 
            if (DateTime.TryParseExact(from, "dd.MM.yyyy", null, DateTimeStyles.None, out dt))
                return dt;
 
            if (DateTime.TryParseExact(from, "dd/MM/yyyy", null, DateTimeStyles.None, out dt))
                return dt;
 
            if (DateTime.TryParseExact(from, "dd MM yyyy", null, DateTimeStyles.None, out dt))
                return dt;
 
            throw new ArgumentException("can not make a date from " + from, "from");
 
        }
}

2. Create the class that will hold one record:

[IgnoreEmptyLines(true)]
[DelimitedRecord(",")]
internal class DestinationReader
{
    //[FieldConverter(ConverterKind.Date,"dd.MM.yyyy")]
    [FieldConverter(typeof(ConvertDate))]
    public DateTime Date;
    [FieldConverter(ConverterKind.Int32)]
    public int StartMiles;
 
    [FieldQuoted(QuoteMode.OptionalForBoth)]
    public string Destination;
 
    [FieldConverter(ConverterKind.Int32)]
    public int  EndMiles;
}

3. Now read the entire string:

string Text = text that comes from the user
string TextDelim = Text.Substring(10, 1);// the date has 10 chars - so the eleven is the separator
while (Text.IndexOf(TextDelim + TextDelim) > 0)//consolidate for 2 delimiters
{
    Text = Text.Replace(TextDelim + TextDelim, TextDelim);
}
DelimitedFileEngine<DestinationReader> flh=new DelimitedFileEngine<DestinationReader>();
flh.Options.Delimiter = TextDelim;
 
var data =flh.ReadString(Text);

In data you have a list of DestinationReader
So for any structured import of data use FileHelpers from http://www.filehelpers.com/

MVC Helper Templates

In my experiences with MVC I have some utilities to share . Some of them are :

DateTime fields
Numeric fields
Watermark
Dropdownlist
more!

Please see the project and give feedback

MvcHelperApplication

Caching in .NET

In every application you have some data that is more read-more, write-once or twice. For example you can have the list of Cities of a country, the list of Countries of the world or list of exchange currency. This data is modified rarely. Also, you can have data that is not very sensitive to be real-time , such as the list of invoices for the day.
In .NET 3.5 you have several options
1. ASP.NET caching – and implementing in other applications with HttpRuntime ( even if MS says “The Cache class is not intended for use outside of ASP.NET applications”)

2. Enterprise caching block : hard to configure

3. memcached , velocity, sharedcache and other third party providers – that comes with their options and configuration

In .NET 4.0 you have a new kid : objectcache and , more important , an implementation : MemoryCache

http://msdn.microsoft.com/en-us/library/system.runtime.caching.memorycache%28v=VS.100%29.aspx

What is very good is that now you can cache in Memory what do you want – and apply easily to your Business Layer. More, the object is a singleton for the application – that is even better (see the test on the final of the post)

What it is missing is an easy implementation for List and an implementation to remove data after a defined time.

So I decided to do my implementation for that (ok, it is wrong to have both implementations in a single class – but you can separate easily )

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Runtime.Caching;
 
namespace CachingData{
 
    /// <summary>
    /// List<int> i = new List<int>() { 1, 10, 100 };
            //CacheData_List<List<int>, int> data = new CacheData_List<List<int>, int>(2);
            //data.Add(i);
            //Assert.AreEqual(3, data.Items().Count, "must be 3");
            //data = new CacheData_List<List<int>, int>();
            //Assert.AreEqual(3, data.Items().Count, "must be 3");
            //Assert.IsTrue(data.ContainsData, "must have data");
            //Thread.Sleep(1000 * 3);
            //Assert.IsFalse(data.ContainsData, "must not have data");
    /// </summary>
    /// <typeparam name="T">and generic ILIST </typeparam>
    /// <typeparam name="U"></typeparam>
    public class CacheData_List<T, U>
        where T:class,IList<U>, new()
 
    {
        /// <summary>
        /// use this for adding in cache
        /// </summary>
        public event EventHandler RemovedCacheItem;
 
        private System.Timers.Timer timerEvent;
        private MemoryCache buffer;
        private int TimeToLiveSeconds;
 
        private DateTimeOffset dto;
        private string Key;
        /// <summary>
        /// default constructor - cache 600 seconds = 10 minutes
        /// </summary>
        public CacheData_List()
            : this(600)
        {
        }
        /// <summary>
        /// constructor cache the mentioned TimeSeconds time
        /// </summary>
        /// <param name="TimeSeconds">value of time for cache</param>
        public CacheData_List(int TimeSeconds)
        {
            TimeToLiveSeconds = TimeSeconds;
            timerEvent=new System.Timers.Timer(TimeToLiveSeconds * 1000);
            timerEvent.AutoReset = true;
            timerEvent.Elapsed += new System.Timers.ElapsedEventHandler(timerEvent_Elapsed);
            dto = new DateTimeOffset(DateTime.UtcNow.AddSeconds(TimeToLiveSeconds));
            Key = typeof(T).ToString();
            buffer = MemoryCache.Default;
        }
 
        void timerEvent_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
        {
            if (RemovedCacheItem != null)
            {
                RemovedCacheItem(this, EventArgs.Empty);
            }
        }
        /// <summary>
        /// remove item from cache
        /// </summary>
        public void Remove()
        {
            if (buffer.Contains(Key))
            {
                buffer.Remove(Key);
 
            }
            dto=new DateTimeOffset(DateTime.UtcNow.AddSeconds(TimeToLiveSeconds));
        }
        /// <summary>
        /// add multiple items to cache
        /// </summary>
        /// <param name="items">items to add to the cache</param>
        public void Add(T items)
        {
 
            if (buffer.Contains(Key))
            {
                T data = Items();
                foreach (var t in data)
                {
                    items.Add(t);
                }
                buffer.Remove(Key);
            }
            buffer.Add(Key, items, dto);
        }
        /// <summary>
        /// add a item to the IList of the cache
        /// </summary>
        /// <param name="item">an item to add</param>
        public void AddItem(U item)
        {
 
            T data=new T();
            if (buffer.Contains(Key))
            {
                data = buffer.Get(Key) as T;
                buffer.Remove(Key);
            }
 
            data.Add(item);
            buffer.Add(Key, data,dto);
        }
        /// <summary>
        /// usefull if you do not intercept the removed event
        /// </summary>
        public bool ContainsData
        {
            get
            {
                return buffer.Contains(Key);
            }
 
        }
        /// <summary>
        /// retrieve items
        /// </summary>
        /// <returns></returns>
        public T Items()
        {
            if (!buffer.Contains(Key))
                return null;
 
            return buffer.Get(Key) as T;
        }
    }
}

Please note that the test for usage is in the summary :

</pre>
List i = new List() { 1, 10, 100 };
CacheData_List <List<int>, int> data = new CacheData_List<List<int>, int>(2);
data.Add(i);
Assert.AreEqual(3, data.Items().Count, "must be 3");
data = new CacheData_List<List<int>, int>();
Assert.AreEqual(3, data.Items().Count, "must be 3");
Assert.IsTrue(data.ContainsData, "must have data");
Thread.Sleep(1000 * 3);
Assert.IsFalse(data.ContainsData, "must not have data");

You can download the file from

http://msprogrammer.serviciipeweb.ro/wp-content/uploads/2010/05/CachingData.zip

(Last Note : for synchonization maybe it was better to lock on readerwriterlockslim

May 3, 2010
7 Comments
Andrei Ignat
full, HowTo

Save settings – with a class that reads from or saves to app.config or web.config

Step 1: Add reference to System.Configuration

Step 2 :Derive your class from ConfigurationSection

Step 3 : Put your values to be retrieved with ConfigurationProperty attribute

Step 4: add a section to your config file and an entry

Step 5 : read with ConfigurationManager.GetSection and convert to your class

Download code

See video

Tag: C#

Andrei Ignat weekly software news(mostly .NET)