Friday, January 14, 2011

Retrieving data as objects using Enterprise library 5.0 database application block

Enterprise library 5 provided new extension which is called Accessors. Accessors execute the given query with parameters mapping and parameter values and also transform the result using output mapper you specified.
There are two types of accessors. SprocAccessor for stored procedure and SqlStringAccessor for SQL string. The most interesting part of accessors is mapping.
Here I give example with SqlStringAccessor. Lets see an simple example of using CreateSqlAccessor.
public IEnumerable<Company> GetCompanies()
          return _database.CreateSqlStringAccessor<Company>(GetCompaniesSQL());
Here company is my created DTO and column definition match with properties of Company class. Here in this case I have not given any custom output mapper and it used default mapper which matches property name and type with column of database and returns me IEnumarable of Customer.
There are two types of output mapper. Row mapper which takes each rows and transform into object so that it returns sequence of these objects.Another one is Result set mappers, takes entire result set and generates  a complete object graph.
Now problem is, I have a column in my Company table “Action” which stores value as Integer but in our code this “Action” is defined as an Enum. So here default mapping is not possible and we need to define a custom row mapper for converting the type of int to Enum type. 
Database application block provides a MapBuilder that make it easy to create a custom output mapper. MapBuilder expose a method BuildAllProperties which creates default output mapping .  For details about output mapping you can see the MSDN article  Now lets see the implementation of row mapping for “Action” column.
public IRowMapper<Company> GetCompanyRowMapper()
          return  MapBuilder<Company>.MapAllProperties().Map(m => m.Action).WithFunc(
                    rec => (CompanyAction)Enum.ToObject(typeof(CompanyAction), rec.GetInt32(rec.GetOrdinal("Action")))).
When we call MappAllProperties ad it gives IMapBuilderContext and after calling build it create RowMapping. Here after getting IMapBuildContext the property “Action” of Company class is mapped with  a  delegate function which works on IDataRecord and convert the value to enum. Here database value 1 is converted with CompanyAction enum value. Now  the GetCompanies function will look like this.
public IEnumerable<Company> GetCompanies()
          return _database.CreateSqlStringAccessor<Company>(GetCompaniesSQL(),
Accessors takes rowmapper as input and it returns all companies. But if I need to get a company with company Id only which will return a single company then I also have to give company id as input parameter and create a parameter mapping.
To create a custom parameter mapping I have implemented IParameterMapper interface and mapping is assigned inside AssignParameters method body.
private class CompanySelectParameterMapper : IParameterMapper
           public void AssignParameters(DbCommand command, object[] parameterValues)
               DbParameter parameter = null;
               parameter = command.CreateParameter();
               parameter.ParameterName = "@Id";
               parameter.Value = parameterValues[0];

Here it convert DbParameter for inputs and assign this to command. I have shown here simple implementation of this mapping.

So the function for getting a single company with company id is
public Company GetCompanyById(int id)
           return _database.CreateSqlStringAccessor<Company>(GetCompanyById(), new CompanySelectParameterMapper(),GetCompanyRowMapper()).Execute(id).SingleOrDefault();
Here you can see I have created an object of parameter mapper and in the Execute() function the values of parameters is defined. So the AssignParameter will be called when Accessor will call the Execute method and populate the command with parameter value.
Here you have seen how to retrieve data as object and how to define custom output and parameter mapping with Accessors. As it create default output row mapping so we do not need to give extra effort to create O/ R mapping all time. SprocAccessor also provide same sets of feature as SqlStringAccessor provides.

Monday, January 10, 2011

Fetching ASP.NET authenticated page with HTTPWebRequest

For some purposes we needed to fetch data from an authenticated page of When I try to browse that page it go to the login page. In the login page there have user name and password field and want to login to the page clicking on submit button.
In this case when user type user name and password and submit then in server side there has code on button click handler to check user name and password. So for authenticating to the page using HTTPWebRequest we need to know how ASP.NET send event to submit click handler. ASP.NET page has two hidden variables understand from server-side which button is clicked.
<input type="hidden" name="__EVENTTARGET" id="__EVENTTARGET" value="" />
<input type="hidden" name="__EVENTARGUMENT" id="__EVENTARGUMENT" value="" />

And also when button is clicked then a javascript  function is called which set the name of the button in __EVENTTARGET and command argument in _EVENTARGUMENT

function __doPostBack(eventTarget, eventArgument) {
if (!theForm.onsubmit || (theForm.onsubmit() != false)) {
theForm.__EVENTTARGET.value = eventTarget;
theForm.__EVENTARGUMENT.value = eventArgument;

So if we set the __EVENTTARGET value as button name then in server side of ASP.NET page life cycle it it raise postback event and call the Button event with the argument. You can see the button argument to understand which event is set to __EVENTARGUMENT hidden variable. The page which we want to authenticate have nothing as command argument. so it go as empty string. So when we request data we have to send username, password, and also __EVENTARGET as button name and   __EVENTARGUMENT as empty string. Then it will call the Button event with user name and password.

Our used HTTP web request class looks like this

public WebPostRequest(string url, CookieContainer  cookieContainer) 
theRequest = (HttpWebRequest)WebRequest.Create(url);
theRequest.CookieContainer = cookieContainer;
theRequest.Method = "POST";
theQueryData = new ArrayList();
public void Add(string key, string value)
theQueryData.Add(String.Format("{0}={1}", key, HttpUtility.UrlEncode(value)));

Here you can see it create a request and set the cookie container with give cookie. As we are authenticating the page so authenticated session is stored in cookie. So we need to assign the cookie container were cookies will be stored so that sending the same cookie we can request other page which we want to actually request.

So for first time when we want to login to the page then the we create the request like

CookieContainer cookieContainer = new CookieContainer(); 
WebPostRequest myPost = new WebPostRequest(http://samplehost/sample/LoginAdmin.aspx, cookieContainer);
myPost.Add("LoginAdmin$UserName", "username");
myPost.Add("LoginAdmin$Password", "password");
myPost.Add("__EVENTTARGET", "LoginAdmin$SubmitButton");
myPost.Add("__EVENTARGUMENT", "");

You can see here a cookie container is added and  trying to authenticate by calling LoginAdmin.aspx page adding query data . Now when we try to GetResponse with post request then it will fill the cookie information in the  cookie container . So next time we will send this cookie container for request and the site will treat me as authenticated user. So the response code here

public string GetResponse() 
{// Set the encoding type
theRequest.ContentType = "application/x-www-form-urlencoded";
// Build a string containing all the parameters
string Parameters = String.Join("&", (String[])theQueryData.ToArray(typeof(string)));
theRequest.ContentLength = Parameters.Length;
// We write the parameters into the request
StreamWriter sw = new StreamWriter(theRequest.GetRequestStream());
// Execute the query
theResponse = (HttpWebResponse)theRequest.GetResponse();
StreamReader sr = new StreamReader(theResponse.GetResponseStream());
HttpStatusCode code = theResponse.StatusCode;
return sr.ReadToEnd();

from the response string you can understand that you have authenticated to the page.

But other target page was not the LoginAdmin.aspx. We called this page for authentication and also get authenticated cookie in our cookie container . So now we can send request again with then same cookie container to get the output of desired page.

myPost = new WebPostRequest("http://samplehost/sample/Targetpage.aspx", cookieContainer); 
myPost.Add("ctl00$cphPage$txtDate", "04/11/2010");
myPost.Add("__EVENTTARGET", "ctl00_cphPage_btnSend");
myPost.Add("__EVENTARGUMENT", "");
string FinalRespose = myPost.GetResponse();

So far I have discussed here how we can request a authenticated authenticated authenticated page using HTTPWebRequest to fetch data from code. After that we can do anything with the retrieved output.