I'm presenting data for users in a grid (ExtJS) with remote sorting and paging. Let's say I have a grid with some Orders. Order entity looks like Order{OrderNumber, Customer, Date, Address{Street, City, PostCode}}. Customer is mapped by NH as relation, Address is mapped as component. Data presented in the grid are flattened to columns named like this: OrderNumber, Customer.Number, Customer.Name, Date, Address.Street, Address.City, Address.PostCode.
User selects a column which he'd like to sort by and the grid sends the field name to server. Now on server side I need to restore backwards what entity property belongs to grid field name and decide if it's just component or if it's relation and build Criteria with CreateAlias + AddOrder etc. This logic is full of code like:
if (gridField=="Customer.Name"){
cri = cri.createAlias("Customer", "customerAlias");
cri.AddOrder(Order.Asc("customerAlias.Name"));
}
This is much simplified, but it neccesarily looks like this at the moment. I'm looking for some generic smarter solution. Any thoughts? The problem I'm facing now is that I can have a convention for transforming entity properties (including nested components and relations), but than I need to have a method how to determine if the field is mapped like component or relation. This would be quite heavy....
It would be quite heavy. I don't see a simple solution, but if you are planning on re-using this a lot, or need something very robust, you could build a system based on reflection.
Another possibility would be to use some T4 templates, but that would only help the 'string' issue, not the association issue.
How about:
cri = cri.CreateAlias( "Customer", "CustomerAlias" );
string sortProperty = gridField.Replace("Customer.", "CustomerAlias.");
cri.AddOrder( Order.Asc(sortProperty) );
Related
I am bootstrapping myself through my very first ASP MVC project, and could use some suggestions regarding the most appropriate (data-side) model binding solution I should pursue. The project is 'small', which really just means I have very limited time for chasing down dead-ends, which cramps my available learning curve. Thanks heaps for reading!
Background: a simple address search app (ASP.NET MVC 3) that sends user form input to a vendor-sourced server, and presents the results returned from the server in a rules-driven format. There is no CRUD-style repository as such; this is an entirely read-only application. The vendor's .NET server API specifies the use DataTable objects (System.Data.DataTable) for both requests and replies.
Currently: I have a prototype under construction to validate server behavior and inform the application's design. There is a conventional MVC data model class for the input form which works great, auto-binding with the view just as you'd expect. When submitted, the controller passes this input model to my vendor API wrapper, which is currently binding to the request table medieval-style:
public DataTable GetGlobalCandidateAddresses(AddressInputModel input)
{
...
DataRow newRow = dataTable.NewRow();
newRow[0] = input.AddressLine1;
newRow[1] = input.AddressLine2;
newRow[2] = input.AddressLine3;
...
dataTable.Rows.Add(newRow);
...
This works fine; the inputs are fixed and have very light validation requirements. However, if there is a modern framework solution for quickly reflecting a DataTable from my model, that would be peachy.
My real conundrum, however, is on the reply. The table returned by the server contains a variable column-set, with any combination of at least 32 possible unordered fields on a per-transaction basis. Some of the column names contain compiler-invalid characters ("status.description") that won't map literally to a model property name. I will also have a need to dynamically map or combine some of the reply fields in the view model, based on a series of rules (address formats vary considerably by country), so not all fields are 1-to-1.
Just to get the prototype fired up and running, I am currently passing the reply DataTable instance all the way back to a strongly-typed view, which spins it out into the display exactly as is. This is nice for quickly validating the server replies, but is not sufficient for the real app (much less satisfying best practices!).
Question: what is my best tooling approach for binding DataTable rows and columns into a proper model class for display in a view, including some custom binding rules, where no underlying database is present?
Virtually all of the training materials I am consuming discuss classic database repository scenarios. The OnModelCreating override available in the Entity Framework seems ideal in some respects, but can you use a DBContext without a DB connection or schema?
If I have to roll my own model binder, are there any tricks I should consider? I've been away from .NET for a while (mostly Java & SQL), so I'm picking up LINQ as I go as well as MVC.
Thanks again for your attention!
Create a poco display model AddressDisplay and do custom object mapping from the data table to the display model. You can use data annotations for formatting but you can also do that in your custom mapping. You shouldn't need to create a custom model binder.
So create two poco models, AddressInput and AddressDisplay, you can use data annotations on AddressInput for validation. When AddressInput is posted back, map it to the outbound data table. When the response is received, map the inbound data table to AddressDisplay and return the view to the user.
I am constanstly having problems with model design in MVC. Mostly all of my projects require some entities that are to be created, edited and deleted. Most of these entities have some common properties like creation date, modified date, author, modified by and in some cases even more descriptive properties are common. Because of that I have one single DB table to store them. For instance, Documents table and we store Invoices, Quotations and other business documents in it. I am using Entity Framework v4 for ORM, where we eventually end up with the Document entity.
How do I modify this entity or do I create a separate DocumentViewModel class for it to support multiple document types with common properties (so some form of inheritance or interface implementation should be implemented)? Besides identifying different document types I also need to have some types to have different Data Annotation rules (attributes).
For instance, Document table has PayDate column. Document type Invoice requires PayDate to be provided but document type Quotation does not.
This is the one single problem I am facing over and over with MVC and so far I've been handling it different every time but cannot decide how to properly handle it to achieve the maximum application maintainability and ease of development.
Have you considered making Documents entity abstract?
From the DB side, you will have Documents table containing just the fields shared by all Invoices/Quoations/etc. This field will have an IDENTITY PK - e.g DocId.
In the other tables, additional meta-data specific to that document can be stored, and the PK is a (non-IDENTITY) field DocId, which is also a FK to the Documents table.
On the EF side, Documents becomes an abstract entity, and the other entities inherit from this entity. This allows a nice OO paradigm to exist, and makes your code more robust.
We are currently using this scheme (EF4/SQL Server).
Your scenario sounds very similar to ours - consider using Abstract Classes.
EDIT
Thought i'd add a bit more info to how i've actually implemented this scenario, to put you on the right track.
As the comments to your Q state, we have little knowledge of your domain, therefore it's hard to make informed opinions. Personally, i chose to make my entity abstract, because certain functionality required a "mixed-bag" of items to be returned in one hit. There are other ways to do this of course (such as a stored procedure), but this allows a nice fluent interface between my UI (which is MVC by the way) and my service layer.
Works like this - here's how i get a single Post:
// var is strongly-typed to a "Post"
var somePost = repository.FindSingle(10);
Here's how i get a mixed-bag of Posts:
// var is strongly-typed to a "ICollection<Post>".
// "Title" is a property on my "Post" abstract POCO
var mixedBagOfPosts = repository.FindAll<Post>(p => p.Title = "Some Title");
Here's how i get a collection of "Reviews" (child of Post):
// var is strongly-typed to a "ICollection<Review>"
// "Rating" is a property on my "Review" POCO (derived from Post)
var reviews = repository.FindAll<Review>(r => r.Rating == 5.00);
The kicker is my repository is implemented with generics, and the type parameter ensures type-safety:
ICollection<T> FindAll<T>(Expression<Func<T,bool>> predicate) where T : Post
And it's implemented like this:
return myContext.Posts.OfType<T>.Where(predicate).ToList();
The OfType causes an inner join to the T (which is the child table), so only those records are returned.
Of course, i also have a service layer mediating between my UI and repository, but this should get you on the right track.
Also, you don't have to go with the whole Expression-predicate thing, i like this because it minimizes the number of methods on my interface, and gives full querying power to my controllers, whilst ensuring the queries are deferred to the point of the service layer, but not further.
If you don't like this, you could of course have regular parameters (string title, etc).
As i said, this architecture suited my domain requirements, so it may not necessarily suit yours, but hopefully it gives you some insight.
You can put a table in your EF model many times and just rename them to the entities you need. Just delete the columns you dont need from those.
For example, put in a Documents entity... now rename it to Invoice. Now add another one, and name it Quotation... on the Quotation, click on PayDate and hit the delete key. You can customize these all you want! You can do the same with other ORMs, just takes a little more work. With NHibernate you would manually create the Models, then map them to the same table, but only map what you need.
Let's start with this basic scenario:
I have a bunch of Tables that are essentially rarely changed Enums (e.g. GeoLocations, Category, etc.) I want to load these into my EF ObjectContext so that I can assign them to entities that reference them as FK. These objects are also used to populate all sorts of dropdown controls. Pretty standard scenarios so far.
Since a new controller is created for each page request in MVC, a new entity context is created and these "enum" objects are loaded repeatedly. I thought about using a static context object across all instances of controllers (or repository object).
But will this require too much locking and therefore actually worsen perf?
Alternatively, I'm thinking of using a static context only for read-only tables. But since entities that reference them must be in the same context anyway, this isn't any different from the above.
I also don't want to get into the business of attaching/detaching these enum objects. Since I believe once I attach a static enum object to an entity, I can't attach it again to another entity??
Please help, I'm quite new to EF + MVC, so am wondering what is the best approach.
Personally, I never have any static Context stuff, etc. For me, when i call the database (CRUD) I use that context for that single transaction/unit of work.
So in this case, what you're suggesting is that you wish to retrieve some data from the databse .. and this data is .. more or less .. read only and doesn't change / static.
Lookup data is a great example of this.
So your Categories never change. Your GeoLocations never change, also.
I would not worry about this concept on the database/persistence level, but on the application level. So, just forget that this data is static/readonly etc.. and just get it. Then, when you're in your application (ie. ASP.NET web MVC controller method or in the global.asax code) THEN you should cache this ... on the UI layer.
If you're doing a nice n-tiered MVC app, which contains
UI layer
Services / Business Logic Layer
Persistence / Database data layer
Then I would cache this in the Middle Tier .. which is called by the UI Layer (ie. the MVC Controller Action .. eg. public void Index())
I think it's important to know how to seperate your concerns .. and the database stuff is should just be that -> CRUD'ish stuff and some unique stored procs when required. Don't worry about caching data, etc. Keep this layer as light as possible and as simple as possible.
Then, your middle Tier (if it exists) or your top tier should worry about what to do with this data -> in this case, cache it because it's very static.
I've implemented something similar using Linq2SQL by retrieving these 'lookup tables' as lists on app startup and storing them in ASP's caching mechanism. By using the ASP cache, I don't have to worry about threading/locking etc. Not sure why you'd need to attach them to a context, something like that could easily be retrieved if necessary via the table PK id.
I believe this is as much a question of what to cache as how. When your are dealing with EF, you can quickly run into problems when you try to persist EF objects across different contexts and attempt to detach/attach those objects. If you are using your own POCO objects with custom t4 templates then this isn't an issue, but if you are using vanilla EF then you will want to create POCO objects for your cache.
For most simple lookup items (i.e numeric primary key and string text description), you can use Dictionary. If you have multiple fields you need to pass and back with the UI then you can build a more complete object model. Since these will be POCO objects they can then be persisted pretty much anywhere and any way you like. I recommend using caching logic outside of your MVC application such that you can easily mock the caching activity for testing. If you have multiple lists you need to cache, you can put them all in one container class that looks something like this:
public class MyCacheContainer
{
public Dictionary<int, string> GeoLocations { get; set; }
public List<Category> Categories { get; set; }
}
The next question is do you really need these objects in your entity model at all. Chances are all you really need are the primary keys (i.e. you create a dropdown list using the keys and values from the dictionary and just post the ID). Therefore you could potentially handle all of the lookups to the textual description in the construction of your view models. That could look something like this:
MyEntityObject item = Context.MyEntityObjects.FirstOrDefault(i => i.Id == id);
MyCacheContainer cache = CacheFactory.GetCache();
MyViewModel model = new MyViewModel { Item = item, GeoLocationDescription = GeoLocations[item.GeoLocationId] };
If you absolutely must have those objects in your context (i.e. if there are referential entities that tie 2 or more other tables together), you can pass that cache container into your data access layer so it can do the proper lookups.
As for assigning "valid" entities, in .Net 4 you can just set the foreign key properties and don't have to actually attach an object (technically you can do this in 3.5, but it requires magic strings to set the keys). If you are using 3.5, you might just try something like this:
myItem.Category = Context.Categories.FirstOrDefault(c => c.id == id);
While this isn't the most elegant solution and does require an extra roundtrip to the DB to get a category you don't really need, it works. Doing a single record lookup based on a primary key should not really be that big of a hit especially if the table is small like the type of lookup data you are talking about.
If you are stuck with 3.5 and don't want to make that extra round trip and you want to go the magic string route, just make sure you use some type of static resource and/or code generator for your magic strings so you don't fat finger them. There are many examples here that show how do assign a new EntityKey to a reference without going to the DB so I won't go into that on this question.
I've got a page which will have about ten drop down lists which are generated from my SQL database. What's the best way to populate them? I was going to use a stored procedure with LINQ to return multiple result sets, but it seems a bit overkill. Is there another way of doing it? Using HtmlHelpers or something like that?
Seeing as though everyone seems to be confused by this, I will elaborate.
This isn't to do with caching, that's not what the problem states
This isn't to do with ASP.NET controls such as DropDownList, I tagged it asp.net-mvc
This isn't to do with code-behind models, I thought that was implicitly obvious by how I tagged this question originally as ASP.NET MVC
The problem is that multiple results sets are required on the page for drop down lists (think HTML!). So I have a drop down list for your favourite breed of badger, a drop down list for how many birthdays you've had, a drop down list for how many clouds are in the sky today. All of these are dynamically populated (please note, I am joking, this is a finance system I work on). I need all of them to be on my view page, but I'd rather NOT use the IMultipleResult return type in a LINQ stored procedure to bring back multiple result sets. It just gets messy.
So in basic, I want about 10 drop down lists on my view page, all of which are populated with data from a database (which constantly change). What is the best way to get them on the view?
I would just pass the required data to the view, either in multiple ViewData dictionaries or as a special view model if you want strongly typed access. Then use HtmlHelper.DropDownList() to display the actual drop downs.
Weakly typed solution
Controller
ViewData["Data1"] = SomeRepository.GetList();
ViewData["Data2"] = SomeRepositoty.GetList();
return View();
View
<%= Html.DropDownList("Data1") %>
<%= Html.DropDownList("Data2") %>
Strongly typed solution
View model
public class DataViewModel
{
public IEnumerable<string> Data1 { get; set; }
public IEnumerable<string> Data2 { get; set;}
}
Controller
var model = SomeRepository.GetModel(); // returns an instance of DataViewModel
return View(model);
View
<%= Html.DropDownList("Data1", new SelectList(Model.Data1)) %>
<%= Html.DropDownList("Data2", new SelectList(Model.Data2)) %>
It depends on the data, if the data in the database is not updated that often, then you could have a process that creates XML files once a day. Then use the XML files as the source to the dropdowns, this would speed up the application and limit the calls to the database server.
This is really a question of data management, not anything to do with HtmlHelpers until you get to the very pointy end of things. Anyhow, the first thing I would ask myself is "how is this data updated and what kind of filtering do I need?"
If this list is pretty much constant, then you could go for a bit of caching.
If this list is pretty fluid, then just pull it out of the database as needed and be done with it. Worry about caching if your DB box starts melting.
Either way you probably want to wrap things up in some sort of LookupService class, but there isn't enough to go on to make any more specific recommendations.
I second Wyatt's recommendation about grabbing from the DB each time if the list is fluid.
However, I'm doing a similar thing (with 10+ dropdowns on each page, all very static... the values will rarely change).
The first version of the application had a helper method for each dropdown list (about 20 total by the end of the project) that grabbed from the respective tables and cached via another helper. Before I started caching, there was no db context available for the view (i created it in the controller and didn't pass it), each dropdown had to create a new connection. This got noticeably slow. Plus, I had some problems with my caching routines, and saving them with 20 magic strings in the cache, etc. Also, I had a separate querying object where I had to manually build the relationships, and having to create the 20 relationships for inner joins was a pain.
So... my new version:
I'm using a single "selectables" table. There's a PK, and a "selectable type" (which I have to admit is a string). There's a selectables enumerable, which makes things a bit cleaner. There's a main getAllSelectables() method that looks for the entire result set in the cach (and gets all rows from the db if its not in the cache) and returns it. Then there's a getSelectables(enum) that grabs out only the relevant values, and a third function getSelectListItems(enum) that calls getSelectables(enum) and returns a ienumerable for the mvc helper function.
Hope that helps,
James
I want to use an example to explain what I want.
Assume I've following DB design:
Item (id, name, categoryID);
Category (id, name);
When user wants to create an Item (fill in form), I'll give a list of categories in a dropdownlist, and when user chooses one of the categories ASP.NET MVC will automatically bind categoryID, to the selected one. I need to present same dropdown list when editing the item with correct selected one.
Question:
But my DB is very big, and it requires around 30-40 (maybe even more) category-like tables, that contain just "id" and "name", and all tables need to be shown in dropdown list while creating some other object, and also needs to be presented while editing the object. Definitely above schema doesn't work, because it's tedious to write same logic 100 times with just different table names. (I'm using Linq2SQL)
Currently my solution is:
Make a view that's based in all such tables and in application I just call a function that construction dropdownlist from that single view. But it's still tedious to change view definition everytime I add a new table.
Do you guys think of a better solution for this tedious work, possibly using reflection or some other tecnologies.
It is not a problem "Definitely above schema doesn't work, because it's tedious to write same logic 100 times with just different table names."
If I were you, I will mark an addition interface on these class using "partial class" feature.
Then, I will write few extension method for the partial class.
If anyone interested in the solution:
I've used reflection to solve this problem.
I use reflection over DataContext to get the Table (by string name), and get its fields and construct the optionlist.