C＃ASP.NET连接到数据库错误

Question

So, i am trying to learn ASP.NET but i am stuck when it comes to DB connections.

I get the following error:

Unable to find the requested .Net Framework Data Provider. It may not be installed.

Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.ArgumentException: Unable to find the requested .Net Framework Data Provider. It may not be installed.

and

Stack Trace:

[ArgumentException: Unable to find the requested .Net Framework Data Provider. It may not be installed.]
System.Data.Common.DbProviderFactories.GetFactory(String providerInvariantName) +1480903
WebMatrix.Data.DbProviderFactoryWrapper.CreateConnection(String connectionString) +63
WebMatrix.Data.<>c__DisplayClass15.b__14() +16
WebMatrix.Data.Database.get_Connection() +19
WebMatrix.Data.Database.EnsureConnectionOpen() +12
WebMatrix.Data.d__0.MoveNext() +66
System.Collections.Generic.List`1..ctor(IEnumerable`1 collection) +381
System.Linq.Enumerable.ToList(IEnumerable`1 source) +58
WebMatrix.Data.Database.Query(String commandText, Object[] parameters) +102
ASP._Page_NewUser_cshtml.Execute() in c:\\Users\\Euaggelos\\Documents\\Visual Studio 2013\\WebSites\\WebSite5\\NewUser.cshtml:20
System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +199
System.Web.WebPages.WebPage.ExecutePageHierarchy(IEnumerable`1 executors) +69
System.Web.WebPages.WebPage.ExecutePageHierarchy() +131
System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +78
System.Web.WebPages.WebPageHttpHandler.ProcessRequestInternal(HttpContextBase httpContext) +116

The problem is that i DO have the .net Framework Data Provider installed.

Here are parts of my code:

<connectionStrings>
    <add name="DB1Entities" connectionString="metadata=res://*/App_Code.Model.csdl|res://*/App_Code.Model.ssdl|res://*/App_Code.Model.msl;provider=System.Data.SqlClient;provider connection string=&quot;data source=(LocalDB)\v11.0;attachdbfilename=|DataDirectory|\DB1Entities.mdf;integrated security=True;connect timeout=30;MultipleActiveResultSets=True;App=EntityFramework&quot;" providerName="System.Data.EntityClient" />
  </connectionStrings>

@using WebMatrix.Data;

@{
    Page.Title = "Add you user";
    Layout = "_Layout.cshtml";
    var db = Database.Open("DB1Entities"); 
    var selectQueryString = "SELECT * FROM Users ORDER BY FirstName";
}



<h1>New user</h1>

<table>
    <tr>
        <th>Id</th>
        <th>First name</th>
        <th>Last name</th>
    </tr>
    @foreach (var row in db.Query(selectQueryString)) <!--THIS IS THE ERROR LINE-->
    {
        <tr>
            <td>@row.Id</td>
            <td>@row.FirstName</td>
            <td>@row.LastName</td>
        </tr>
    }
</table> 

Answer 1

You might need to add this to your app.config file

  <system.data>
<DbProviderFactories>
  <remove invariant="System.Data.SqlServerCe.4.0" />
  <add name="Microsoft SQL Server Compact Data Provider 4.0" invariant="System.Data.SqlServerCe.4.0" description=".NET Framework Data Provider for Microsoft SQL Server Compact" type="System.Data.SqlServerCe.SqlCeProviderFactory, System.Data.SqlServerCe, Version=4.0.0.0, Culture=neutral, PublicKeyToken=89845dcd8080cc91" />
</DbProviderFactories>

Answer 2

Your connection string is for an Entity Framework Database First project. However, you don't appear to be using EF in your WebMatrix site. You are using standard SQL to query the database. Change the connection string to a plain one:

<connectionStrings>
    <add name="DB1Entities" connectionString="data source=LocalDB)\v11.0;attachdbfilename=|DataDirectory|\DB1Entities.mdf;integrated security=True;" providerName="System.Data.SqlClient" />
</connectionStrings>

If you want to use Entity Framework with a Web Pages project, you should use the Code First approach as detailed in my article here: http://www.mikesdotnetting.com/article/182/entity-framework-code-first-development-with-webmatrix