I have these two tables in MySql:
[Person]
PersonId
NameFirst
NameLast
[Email]
EmailId
PersonId
EmailAddress
In VS2010, I added a new item, ADO.NET Entity Data Model. I connect to MySql and "drag-and-drop" my the two tables into the .edmx designer. Great! It has relationships and all.
Now I want to bind something like this to a Gridview WITHOUT using an EntityDataSource control:
SELECT * FROM Person INNER JOIN Email ON Person.PersonId = Email.PersonId
How am I to do this programmatically using the modern approach? I noticed in my .edmx, the tables have "Navigation Properties" and the related tables are listed there. I just don't know the concept and syntax to use it since my skills are still "DataSet-SQL Queries-DataAdapter" based.
You can start with something like this:
var query = from x in Context.Persons // Entity set on your context
from y in x.Emails // Navigation property
select new PersonProjection // Your custom class for flattened result
{
PersonId = x.PersonId,
FirstName = x.NameFirst,
LastName = x.NameLast,
EmailId = y.EmailId,
EmailAddress= y.EmailAddress
};
gridView.DataSource = query.ToList();
gridView.DataBind();
Related
What is EntityReference and QueryExpression? Please give me some simple examples.
EntityReference
It is used for lookup fields in
365 – e.g. to link records via a 1 to many relationship. The lookup
field is shown on the ‘child’. You need to specify the ‘parent’ entity
type and record id.
For example if you are creating a accountand want to set the primary contact.
Entity account = new Entity("account");
account["name"] = "James Account";
account["primarycontactid"] = new EntityReference("contact", contactId);
service.Create(account);
QueryExpression
QueryExpression provides an object model to construct a query. Queries
can also be created using FetchXML, a proprietary XML based query
language.
For example of you wanted to retrieve all contacts full name and telephone number.
QueryExpression query = new QueryExpression()
{
Distinct = false,
EntityName = Contact.EntityLogicalName,
ColumnSet = new ColumnSet("fullname", "address1_telephone1"),
};
DataCollection<Entity> entityCollection = _service.RetrieveMultiple(query).Entities;
I was able to get the columns names by using this:
var props = typeof(FMCSA_NPR).GetProperties();
But it is also giving me the names of other tables which have a foreign relation with the specified table.
Is there a way by which I can only get the column names? What do we call column names when referring table as entity in Entity Model?
You can list the non-navigation properties of entities by accessing the conceptual model (CSpace):
var oc = ((IObjectContextAdapter)db).ObjectContext;
var cs = oc.MetadataWorkspace.GetEntityContainer(oc.DefaultContainerName,
DataSpace.CSpace);
foreach (var entitySet in cs.EntitySets)
{
var props = string.Join(",", entitySet.ElementType.Properties);
Trace.WriteLine(string.Format("{0}: {1}", entitySet.Name, props));
}
(Where db is your DbContext object).
I am working on an example asp.net project using MVC, but my database is a live one which I can't make changes to (technically it's the test version of this database but my point is changes to the database aren't possible).
I use the UserID from the asp_Users table to store who makes changes to various aspects of the system, and I want to start showing the user name in various front-end tables, but how do I link the tables to get this user name?
So to clarify, I'm going to want to do this for several tables throughout the system so I was hoping I could do it using LINQ.
I can get the info I want from using the join query, but how do I pass this to my View to use?
var plans = from users in db.aspnet_Users
join import in db.Plan_Imports
on users.UserId.ToString()
equals import.User_ID
select new
{
Date = import.Date,
UserName = users.UserName
};
Sample tables
asp_Users
UserID
UserName
...
table1
ID
field1
field2
...
User_ID <--- ref to asp_Users
table2
ID
field1
field2
...
User_ID <--- ref to asp_Users
I would create a ViewModel for each view.
ViewModel is just a POCO class
public class PlanViewModel
{
public string UserName { set;get;}
public DateTime ImportDate { set;get;}
}
Then Get the Data to this ViewModel/Collection of ViewModel using LINQ Projections from your query.
public ActionResutl Show()
{
var plans = (from users in db.aspnet_Users
join import in db.Plan_Imports
on users.UserId.ToString()
equals import.User_ID
select new PlanViewModel
{
ImportDate = import.Date,
UserName = users.UserName
}).ToList();
return View(plans);
}
Now Lets make our view strongly typed to a collection of our PlanViewModel
#model List<PlanViewModel>
#foreach(var plan in Model)
{
<p>#plan.UserName</p>
<p>#plan.ImportDate.ToString()</p>
}
The solution provided by Shyju worked perfectly, and it wasn't too complex to do, however I decided that I didn't think using LINQ was appropriate in this case as the code was getting out of hand for what should be a simple call.
What I did instead was use a stored procedure to get the information, and saved it to a complex object which I passed to my view.
The code is now much neater and easier to manage, as the code above became just
var plans = db.SP_SelectImports();
Read more about stored procedure mapping here: http://dotnet.dzone.com/news/mapping-stored-procedure
My first MVC3 EF 4.2 site and I'm confused on some things, currently on ViewModels when querying and saving. Please correct me if I explain this poorly, i'm not sure how to term this. The .edmx automatically created the table classes but I read it was better to create a ViewModel, considering I need to join tables to display/edit my Product completely. The controller code below is where I join tables to output a Product to edit, and then save. My question - what is the right way to save the Product, to the Product.cs model generated by DbContext or my own ProductViewModel.cs?
Is there an easier method to query a product and join the tables and then map to the viewmodels parameters, or do I keep doing all this in the controller like below?
I also want to save/update the product each time someone views/clicks on the product, so I wasn't sure if I create a separate ViewModel for updating just that parameter or again, use the Product model.
Hope that makes sense! I can explain further if needed.
private SiteForgeEntities db = new SiteForgeEntities();
public ActionResult Edit(int id)
{
var viewModel = (
from a in db.Products
join b in db.Sites
on a.SiteId equals b.SiteId
join c in db.Sections
on a.SectionId equals c.SectionId
join d in db.Affiliates
on a.AffiliateId equals d.AffiliateId
select new ProductViewModel()
{
ProductId = a.ProductId,
Product = a.Product,
Description = a.Description,
Image = a.Image,
Price = a.Price,
Clicks = a.Clicks,
Link = a.Link,
Site = b.Site,
Section = c.Section,
Affiliate = d.Affiliate
}).Single(x => x.ProductId == id);
return View(viewModel);
}
[HttpPost]
public ActionResult Edit(Product product)
{
...update database...do I pass in and save back to Product or my ProductViewModel
}
You use ViewModel to pass multiple models to the view, but when you save data, you need to save it to the appropriate model. If you are adding or modifying products, you will add items to products (using your DbContext). If you have one-to-many relationship defined between two models (in your Product.cs model you might have a property declared as:
public virtual ICollection<SomeOtherModel> SomeOtherData { get; set; }
you can use this to build a table instead of passing everything in a ViewModel. There is a nice tutorial here regarding the CRUD operations using EF4. Have a look at these short tutorials that can give you an idea about your strategy http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc.
I have this contact list which I'm building using LINQ to SQL. The query to get a list of contacts is:
return db.Contacts.ToList();
In the list I also want to display each contact's primary e-mail address. To do this I first rewrite my query:
return (from db.Contacts
select c).ToList();
I found this nice way to do left joins:
return (from db.Contacts
from ce in ContactEmails.Where(x => x.ContactID == c.ContactID && c.IsPrimary).DefaultIfEmpty()
select c).ToList();
But now I want to add this PrimaryEmailAddress to my Contact object. To do this I have added a property (PrimaryEmailAddress) to the generated Contact class, using a partial class.
Is it possible in the LINQ query to add the value to c.PrimaryEmailAddress somehow? My solution right now is to create anonymous objects and then iterate them.
Here's one way to do it:
In your entity designer, create an association between your Contact class and your ContactEmail class (just guessing at your class names here). Here are some instructions on creating an association.
Then, configure your DataContext to load only your primary ContactEmail. Here are some instructions on filtering child data at the DataContext level.
And here is an entirely different way to do it:
In your partial Contact class, in your partial OnLoaded() method, query the primary ContactEmail. For example:
partial void OnLoaded()
{
// get your DataContext here
this.PrimaryContactEmail = db.ContactEmails
.Where(ce => ce.ContactID == this.ContactID && ce.IsPrimary)
.SingleOrDefault();
}