I am new to MVC. and I'm trying to find my way through online tutorials.
being said that,
I have a table A (a1,a2,a_b1)
and a table B (b1,b2)
and a_b1 is a foreign key from B.b1.
I generated the List view in Visual studio, using its template.
I have access to a1, and a2 fields of table A.
<%=Html.Encode(item.a1) %> and <%=Html.Encode(item.a2) %>
but when I try to access the A.a_b1 value (NOT the reference to table B), I only get the reference to an object from table B.
Thanks Kirill
I don't know what are CodeFirst, ModelFirst or DatabaseFirst.
I have these tables, and used visual studio, and Linq to generate the class for tables A and B.
so A.a1, A.a2 show up in the object created.
and I have A.B, and A.BReference in the fields
I think there should be a way to access the value of the column not the reference.
Can you please help me?
I don't want to perform the join, just need the value.
I tried my best to be specific but please let me know if this is not clear.
Thanks
EDIT:
I used ADO.Net Entity Data Model to generate objects associated with my tables.
In my controller I have :
A sample1=repository.search(id);
string s1 = sample1.a1;
string s2 = sample1.a2;
string s3 = sample1.a_b1; (ERROR)
Instead I have
sample1.B (an object of type B)
and
sample1.BReference (object of type EntityReference<B>)
Answer for those who ran into the same problem:
I defined a new class A_text that has all the fields of A. (including a_b1)
and in Select, I used :
var result = from pt in db.A
where pt.id== id
select new A_text
{
id= pt.id,
a1= pt.a1,
a2 = pt.a2,
a_b1= pt.a_b1.id
};
return (result.FirstOrDefault());
I'm not sure about the efficiency compared to the
db.Search(id);
but seems ok so far.
Related
I am new to entity framework and I am trying to get my head around it. I am used to writing stored procedures which have all the data I need on a example by example basis.
I am under the impression that I can get all values from a particular table including the foreign key values direct using entity framework without having to write a select query which joins the data.
I have the following in my controller
public ActionResult Patient()
{
using (var context = new WaysToWellnessDB())
{
var patients = context.Patients.ToList();
return View(patients);
}
}
In my view I have the following
#foreach (var item in Model)
{
<p>
#item.FirstName #item.Surname #item.Gender.GenderDesc
</p>
}
I have two tables, Patient and Gender, GenderId is a foreign key which I am trying to get the GenderDesc from that table.
I am getting the following message
The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.
Can someone explain why I cannot access GenderDesc. It does work if I remove the using() around my context, but I don't really want to leave that open, is there a way to get this to work still having the using around?
Thanks in advance.
Correct, you have disposed of the context as it is within a using statement, so anything you try to access from then on will not be able to be lazy loaded. The disadvantage with lazy loading is that it will perform a query for the gender for every patient you are iterating over, which is handy, but bad! I would load the related table at query time using Include.
You'll need a new import:
using System.Data.Entity;
And then include the related table:
var patients = context.Patients.Include(p => p.Gender).ToList();
That will result in a query which will join to your "Gender" table and you should be able to output item.Gender.GenderDesc in your view.
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.
Getting an error client side with breeze: "Cannot call method 'map' of undefined" when trying to pull over some data. The difference between this action and one that works is that this action is calling a stored procedure and returning ObjectResult<T> instead of DbSet<T>.
Might this be why I get an error? Using Chrome Developer tools, I do see that the breeze controller is returning json data.
I have created a complex model type in the edmx for mapping the rows returned from the stored procedure.
The action in the breeze controller has a return type of IEnumerable<T>.
I experienced the same error when using an EF complex type. A workaround was to create a view in my database instead of using a complex type, set the stored procedure to return a type of the new view which had a primary key and then it worked. It would seem that breeze requires entities to have a primary key defined.
Hm... not quite sure what is happening, so just guessing here, but try adding an AsQueryable() to the result returned, and changing the result type to a IQueryable.
We don't have any stored proc tests for breeze yet, but this is impetus for me to add some :)
I had the very same issue, but thank God I figured out a solution. Instead of using a stored procedure, you should use a view, as Breeze recognizes views as DbSet<T>, just like tables. Say you have a SQL server table that contains two tables Customers and Orders.
Customers (**CustomerId**, FirstName, LastName)
Orders (OrderId, #CustomerId, OrderDate, OrderTotal)
Now, say you want a query that returns orders by CustomerId. Usually, you would do that in a stored procedure, but as I said, you need to use a view instead. So the query will look like this in the view.
Select o.OrderId, c.CustomerId, o.OrderDate, o.OrderTotal
from dbo.Orders o inner join dbo.Customers c on c.CustomerId = o.CustomerId
Notice there is no filtering (where ...). So:
i. Create a [general] view that includes the filtering key(s) and name it, say, OrdersByCustomers
ii. Add the OrdersByCustomers view to the entity model in your VS project
iii. Add the entity to the Breeze controller, as such:
public IQueryable<OrdersByCustomers> OrdersByCustomerId(int id)
{
return _contextProvider.Context.OrdersByCustomers
.Where(r => r.CustomerId == id);
}
Notice the .Where(r => r.CustomerId == id) filter. We could do it in the data service file, but because we want the user to see only his personal data, we need to filter from the server so it only returns his data.
iv. Now, that the entity is set in the controller, you may invoke it in the data service file, as such:
var getOrdersByCustomerId = function(orderObservable, id)
{
var query = breeze.EntityQuery.from('OrdersByCustomerId')
.WithParameters({ CustomerId: id });
return manager.executeQuery(query)
.then(function(data) {
if (orderObservable) orderObservable(data.results);
}
.fail(function(e) {
logError('Retrieve Data Failed');
}
}
v. You probably know what to do next from here.
Hope it helps.
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 have the following sample code which gets a list of values from a table in the DB and binds them to a checkbox list.
var db = new DBContext();
db.Entity1.ToList().ForEach(
x => CheckBoxList1.Items.Add(new ListItem(x.Value, x.ID));
I have about 10 checkboxlists like these and I dont want to repeat the code. I'm trying to extract a method out of it and use it for all checkboxes. Is it possible to load an entity by a string name? Something like -
db.Load("Entity1").ToList().ForEach...
So I can pass in the entity name and the checkbox list and do the foreach loop in the method and bind the items, like this -
void BindValues(string entityName, CheckBoxList checkBoxList)
{
db.Load("Entity1").ToList().ForEach(
x => checkBoxList.Items.Add(new ListItem(x.Value, x.ID)));
}
Thank you.
In Code First the DbContext exposes a .Set() or .Set(Type) method to get a handle on the table. So assuming straight EF exposes the same, and you are happy to access your lists by their entity type rather than a string, this would work for you.