In my ASP MVC application I'm using standard SQL (rather that Linq to SQL or other ORM) to query my database.
I would like to pass the database results to my view and iterate over the results in my view. But I'm not sure how to do this. Every example I've seen passes some string or uses L2S. I would like to pass something like nested Hashtables, but the only thing I can think of is to pass an SqlDataReader object to the view, but this sounds like a really bad idea.
How would I go about displaying my database results from a standard SQL query to my view? I would really like use Linq or other ORM, but requirements dictate we don't (don't ask me why, I don't understand). I'm doing this in VB. I'll try by best to convert any C# examples provided.
You could create simple classes for the data you want to transfer and then populate a List of objects in your controller from a data reader manually, and then pass this to your View - e.g. (C# but this should be easy to convert)
// open your connection / datareader etc.
List<Customer> customers = new List<Customer>();
while(dataReader.Read())
{
Customer c = new Customer();
c.Id = dataReader.GetInt32(0);
c.Name = dataReader.GetString(1);
// etc (you might want to use string indexers instead of ints for the get methods)
customers.Add(c);
}
// close and dispose your datareader / connection etc as usual
return View("List", customers);
MVC is about separation of concerns. Passing SqlDataReaders, DataTables, or whatever class that resides in the System.Data namespace to a view is not a good idea. You need to define a model which might talk to the database, and a controller which will pass this model to the view. If your company policy says don't use an ORM then maybe classic WebForms are better suited to your scenario than the MVC pattern.
I agree with Rashack. This article explains it in some detail.link text
In a nutshell, here's how to do it using DataTable and DataReader:
private DataTable GetData()
{
DataTable dt = new DataTable();
using (SqlConnection connection
= new SqlConnection("ConnectionString"))
using (SqlCommand command = new SqlCommand())
{
command.Connection = connection;
command.CommandText = "SELECT * FROM Customers";
connection.Open();
using (SqlDataReader reader =
command.ExecuteReader
(CommandBehavior.CloseConnection))
{
dt.Load(reader);
}
}
return dt;
}
Then, you can read that DataTable into an entity object that you pass around.
I think you'll find this can yield much better performance than using Linq or an ORM.
Try using DataTables - DataTable can load data from IDataReader... (I think the method's called Load)
You could create your own Data Transfer Object classes and populate instances of them using ADO.Net code. These DTO classes would be simple POCO-style classes that just contained property get/set accessors, no methods. Using POCO objects is arguably preferable to DataSets/DataTables as they are lightweight (no superfluous state) and are more intuitive to work with from an object-oriented perspective.
Related
I am working on an ASP.NET MVC 4 web application. I am using Entity Framework as the data access layer, using database first approach (.edmx file).
Currently I have a problem in join tables that are defined inside two different databases (i.e. I have two .edmx files).
For example if I want to join tables I am performing the following query:-
public ActionResult AutoComplete(string term)
{
var tech = repository.AllFindTechnolog(term).Take(100);//Call to the first database
var resources = repository.GetResources(tech.Select(a => a.IT360ID.Value).ToArray(), false);//call to the second database
var query = from techItems in tech
join resourcesItems in resources
on techItems.IT360ID.Value equals resourcesItems.RESOURCEID // join based on db2ID
orderby techItems.PartialTag
select new //code goes here
return Json(query, JsonRequestBehavior.AllowGet);
}
I will have two separate calls to the database, and a join inside the application server, which is not the best performance-oriented solution. Ideally the joins will happen completely inside the database engine.
I know that a stored procedure will allow me to join tables from different databases purely on the server, but I do not want to use SP because it will make my code less maintainable and less testable.
So I am searching for a solution where I can do the join using entity framework and to result in a single database join?
If you want to do it with a single database call you will have to create a View in the database that joins the 2 tables from separate db's. Once the view is created you can add it to EF as a single object, which you can manipulate further and Query off of. The view will basically be a table and it will be easily maintable and easy to bind to a strongly typed model
Another way ,similiar like you have posted, you can query separate .edmx files and then join them.
Yes, there is 2 calls to the database but it shouldn't be that expensive and probably won't notice a difference.
using(var db = new MyEntities())
using (var db2 = new MyEntities2())
{
var one = db.Table1.AsEnumerable();
var two = db2.Table2.AsEnumerable();
var result = from o in one
join t in two on o.Id equals t.Id
// blah blah
}
#CSharper's answer is close. As #Oliver mentioned in the comments, IEnumerable loads the table into application memory, leading to crashes if you have a large database.
The solution is to use IQueryable, which can be called with LINQ - this produces SQL which is much faster.
// This is a generic method, modify to your needs
public ActionResult Details(int? id)
var one = db.Table1.AsQueryable();
var two = db2.Table2.AsQueryable();
// since you're using MVC EF, I assume you want to put this in a viewmodel
// (in this case ObjectCombined)
// assume "id" is passed as parameter
Object1 result1 = (from o in one where one.id == id select o).Single();
Object2 result2 = (from t in two where t.id == o.id select t).Single();
ObjectCombined result = new ObjectCombined(result1, result2);
return View(result);
}
Might I suggest that you look into using a synonym in your database. For instance, you can create a synonym to the resources table in the database that your tech table is located. This will ensure that you will not need to maintain 2 EDMX files. Instead you can have a single EDMX file and you can simply join your tech table to the synonym of the resource table and voila - you are on your way.
UPDATE: Please note that if you are using synonyms there is an extra bit of work you will need to do to the EDMX file to get it working in Entity Framework. Here is a blog post that was put out by a programmer who got it to work. Here is the original stackoverflow question she asked.
HAPPY CODING!!! :)
you can create a view or a stored procedure, your sql statement can then make cross db query just make sure your credentials can DML or DDL on both db. otherwise try the nested using entities that will make sure you will not get the linq bug when you dont declare the db entity inside a using statement.
I'm trying to return a JSON list of stuff from my server via an ASP.NET MVC front layer:
var stuff = repo.GetStuff();
return Json(stuff);
However, instead of the expected JSON, I get an error message stating
A circular reference was detected while serializing an object of type 'System.Reflection.RuntimeModule'.
I think I've found where this happens, but to explain it I need a simple example domain model as follows:
I am (lazily?) loading a selection of documents from NHibernate, like so:
var session = getNHibernateSession();
var query = new NhQueryable<Document>(session.GetSessionImplementation());
var docs = query.ToList().AsEnumerable();
I then pass the documents to return a JsonResult in my controller:
return Json(docs, JsonRequestBehavior.AllowGet);
Now, when Json() serailizes the collection, it walks over the properties of a document, finds a person. It serializes that person, and finds a project. It serializes the project, and finds - that's right - the person again! Since I'm lazy loading, it can just keep walking for ever if nothing stops it, but it's stopped by a circular reference error.
I don't really need to go all these levels down (I'd be fine without loading the project in the first place) - can I somehow affect how Json() serializes this collection, to not go further than, say, 2 levels down? I've googled around a little, but most of what I find seems to be from people who decided to use a serializing library directly, rather than just using the built-in functionality in .NET MVC. (Note: The solution to this problem must be possible to apply specifically to this case, since I might want to get JSON lists of people, including projects, somewhere else in the application...)
If you are retrieving Json, you have a service api. You have to design the api besides the implementation. Does the page that will be using it need all those fields and collections? probably not. What about adding more properties for other features and services? They will start appear in all the requests.
What you need is to use a ViewModel or just an anonymous type with the desired structure:
var session = getNHibernateSession();
var query = new NhQueryable<Document>(session.GetSessionImplementation());
var docs = query.ToList();
var result = query.Select(x => new {
x.Id,
x.Name,
People = new { p.Id,
p.Name,
p.Title
}
});
return Json( result, JsonRequestBehavior.AllowGet);
This way you can control what is being rendered and how.
It's already been answered here.
Also, it's generally a bad idea to expose your domain entities like this. If it's for read-only purposes it might not be so bad, but if any of your action methods accept a domain entity, then a specifically formatted request can overwrite properties on your domain entity that you don't want to (such as your PK).
To preserve object references in JSON, add the following code to Application_Start method in the Global.asax file:
var json = GlobalConfiguration.Configuration.Formatters.JsonFormatter;
json.SerializerSettings.PreserveReferencesHandling = Newtonsoft.Json.PreserveReferencesHandling.All;
I am new to MVC, so please excuse me if my question sounds silly or too simple. I am using Entity Data Model for database access. So in my Models folder, I have added an EDMX file and I can access the model classes from my controllers and strongly typed views. The problem arises when I access more than one table in my controller e.g.
If I have following tables in my DB :
Departments(DepartmentID, DepartmentName, DepartmentPhone)
Insurances(InsuranceID, InsuranceName, InsuranceAddress)
Employees(EmployeeID, EmpFName, EmpLName, DepartmentID, InsuranceID)
And I want to display a list of Employees with their department and insurance information.
In my Controller's Action Method I access the DB using EDM and get the information in an anonymous type:
using (var context = new MyEntities())
{
var model = (from d in context.Departments
join e in context.Employees on d.DepartmentID equals e.DepartmentID
join I in context.Insurances on I.InsuranceID equals e.InsuranceID
select new
{
DepartmentID = d.DepartmentID,
EmployeeID= e.EmployeeID,
EmpFName= e.EmpFName,
EmpLName= e.EmpLName,
DepartmentName= d.DepartmentName,
InsuranceName= I.InsuranceName
}).ToList();
return View(model);
}
I don't have a class of this anonymous type in my Model folder so I can't create a strongly typed view. So what is the best way to pass this list to the View?. Using viewbag will be an overkill if the collection is too large. Creating a new Model for this anonymous class doesn't sound right as it needs to be updated all the time if I change my selection in Controllers Action Method.
All suggestions are welcomed. I tried looking through other questions on SO but couldn't find anything relevant.
Thanks.
I don't have a class of this anonymous type in my Model folder so I
can't create a strongly typed view
Right click on your project, Add New Class ... and now you have a type in your Model folder. This is the way to go in ASP.NET MVC => view models.
And then obviously you pass this type to your view:
select new MyViewModel
{
DepartmentID = d.DepartmentID,
EmployeeID = e.EmployeeID,
EmpFName = e.EmpFName,
EmpLName = e.EmpLName,
DepartmentName = d.DepartmentName,
InsuranceName = I.InsuranceName
}).ToList();
And of course now your view becomes strongly typed to this view model:
#model IEnumerable<MyViewModel>
...
I'm afraid that predefined strongly-typed ViewModels are the way to go. It is a pain to have to update seemingly duplicate code in multiple places but in my experience it's only a problem for smaller projects. As the project grows you begin to see differences between database model objects (entities) and the viewmodels passed to your views, such as Validation and processing attributes and view-specific data, and when you get to that point you begin to prefer having separate Entity and ViewModel definitions.
However, back on-topic: an alternative solution to your problem is to use reflection to convert an anonymous type into a Dictionary<String,Object> object. Note that ASP.NET MVC does this for converting new { foo = "bar" }-syntax expressions into dictionaries for Route Values and HTML attributes already. Performance is acceptable, but don't try to do it for 10,000 objects for a single HTTP request otherwise you might get bogged down.
Here's what the code for that would look like:
Object anonymousType = new { whatever = "foo" };
Dictionary<String,Object> dict = new Dictionary<String,Object>();
foreach (PropertyDescriptor descriptor in TypeDescriptor.GetProperties(anonymousType )) {
Object value = descriptor.GetValue(anonymousType );
dict.Add( descriptor.Name, value );
}
Of course this means that your Views won't benefit from compile-time type-checking and you'll have to maintain a documented list of dictionary keys (assuming you aren't iterating over keys in your view).
I'll note that I am surprised Microsoft didn't make anonymous types automatically implement IDictionary because it seems natural.
dynamic type is your friend.
You can declare your view as loosely typed, having a dynamic as your model
#model dynamic
You will access model properties as you do in strongly typed view
<h1>Model.DepartmentId</h1> - <h2>Model.DepartmentName</h2>
<span>Model.EmployeeId</span>
The problem thought, that dynamics contains internal properties, if you are using MVC2 you need a little trick to make it work. But seems for MVC3 and higher, it's not longer required.
I'm using LINQ to model my database, but I'm writing it by hand (Steve Sanderson recommends this in his ASP.NET MVC book). What I need to know is what's happening when you create an EntityRef, and how it's referenced. If I create my queries manually (without using LINQ), but use LINQ to model it, and I bring back just the ID of something, then reference the actual table column using EntityRef in the view, does it do the join, or does it re-query the database for that bit of information?
To clear things up, if I have this in my repository:
public IEnumerable<MyTable> ListMyTable(int? myColumnVar)
{
string query = "SELECT * FROM MyTable WHERE MyColumn = {0}";
return this.ExecuteQuery<MyTable>(query, myColumnVar);
}
and then in my controller I do this:
IEnumerable<MyTable> mytables = _contractsControlService.ListMyTable(1);
return View(mytables);
then in my view I do things like
<%=tbl.Ref.MyColumn %>
I'm referencing something set out by the LINQ model, but isn't actually in the table output. How does it get that data?
To clear things up further, we're using systems which require ultimate speed, so the LINQ-to-SQL is too slow for us, hence why we're using direct queries in our repository. I wouldn't mind using this EntityRef business if only I knew what was happening underneath.
You have most likely used the Object Relational designer to create an entity class for the Ref entity and an association between the MyTable and the Ref entity. You can also do that manually by creating the appropriate entity classes and using attributes to map the classes to the database schema. You can read the details in How to: Customize Entity Classes by Using the Code Editor (LINQ to SQL) on MSDN.
In your generated (or handwritten) code you will find some attributes:
[Table(Name="dbo.Ref")]
public partial class Ref : INotifyPropertyChanging, INotifyPropertyChanged
and
public partial class MyTable: INotifyPropertyChanging, INotifyPropertyChanged
{
[Association(Name="Ref_MyTable", Storage="_Ref", ThisKey="RefId",
OtherKey="Id", IsForeignKey=true)]
public Ref Ref
{
get
...
The entity classes combined with the attributes enables the Linq-to-Sql framework to retrieve entity classes directly from the database.
If you want to monitor the SQL genereated by Linq-to-Sql you can assign the DataContext.Log property:
context.Log = Console.Out;
In your example, navigating from MyTable to Ref, probably generates SQL along these lines:
SELECT Id, Field1, Field2, Field3
FROM Ref
WHERE Id = #RefId
how should i load the table "Setting" into an asp.net mvc so that i can use it as a reference setting for the whole application.
Is there anyway to save the memory and usage to do this problem? In my understanding, if i have settings in database, i will have to make the program load the table into a variable, then call out. But is there anyway to save a query from being waste?
im using linq to sql
Thanks
Yes, if you use a proper ORM layer, like NHibernate (for instance with Fluent), which can cache the calls (SQL queries) to the settings table for you fully automatically. And you'll handle the tables without any SQL, only as calls to methods of classes.
However, it requires learning NHibernate, which can take a bit getting used to.
It is not possible to get the data of the Settings table from the database without issuing a query to the database. But you can prevent the tedious use of mapping the result to objects by using an ORM.
If you take both NHibernate and FluentNHibernate, it looks something like this for MS SQL Server 2008:
// this depends on your implementation, I assume a Settings class with
// simple getters and setters that map directly to the table. Use
// Fluent to do the mapping (see link) automatically through AutoMappings
// example of using AutoMappings plus configuration of linking to DB:
ISessionFactory sessionFactory = Fluently.Configure()
.Database(
MsSqlConfiguration.MsSql2008
.ConnectionString(c =>
c.Server("123.12.21.321")
.Database("db_name")
.Username("db_user_with_access_to_db")
.Password("passwordhere")
)
)
.Mappings(m =>
m.AutoMappings.Add(AutoMap.AssemblyOf<Logo>()
.Where(t => t.Namespace == "YourNamespace.Entities"))
)
.BuildSessionFactory();
// example of a Settings class:
public class Settings
{
public int Id { get; private set; }
public int BackgroundColor { get; set }
// etc
}
// example of getting a session, retrieving data, changing/saving data
ISession session = sessionFactory.OpenSession(); // session for getting data from DB
Setting mySetting = session.Get<Setting>(someId);
mySetting.BackgroundColor = 0xAA44DD;
var transaction = session.BeginTransaction();
session.SaveOrUpdate(mySetting);
transaction.Commit();
// how it looks like if you use Generics and a little Dao class to wrap it all up:
Dao<Settings> daoSettings = new Dao<Settings>();
Settings someSettings = daoSettings.Get(someIdHere);
Settings userSettings = daoSettings.Get(new User("John"));
List<Settings> allSettings = daoSettings.GetAll();
int BackgroundColor = userSettings.BackgroundColor; // any of the columns here
userSettings.BackgroundColor = 0x45DA8E;
daoSettings.Save(userSettings);
Other ORMs exist, NHibernate may be a bit overkill if this is a one-time only situation and if you never did this before. However, it has an automatic level-1 and level-2 cache to prevent any unnecessary roundtrips to the database. It is currently (allegedly?) the industry leading open source ORM solution.
Update: added simple code example and links to NH/Fluent