I have a constructed a model using code first in C#. The model literally represents a container element for a website building application, in other words, the model defines a Div tag or some such HTML element. Like a Div tag which can contain multiple child elements, I have tried to represent this in my model, but the scaffolding to the DB, does not give me what I'd expect.
I should get a new many to many joins table, but instead I only get a single column in the DB which expects a single int data type.
Here is the model:
public class ElementContainer
{
public int ElementContainerID { get; set; }
public int PageId { get; set; }
public int? ParentElementContainerID { get; set; }
public string ElementContainerName { get; set; }
public ElementType ElementType { get; set; }
public string ElementClass { get; set; }
public PageAsset PageAsset { get; set; } // content of container
public List<ElementContainer> NestedContainers { get; set; }
}
The last line is the self-referential attribute which just appears as a column called ElementContainer_ElementContainerID
Thanks in advance!
I agree with Bahman, DB first is easier.
While I haven't tried to do what you are trying, your code looks like a self-Join that would do exactly what you describe.
This is a One-to-Many relationship. EF Navigation will pull a List of all nested children containers.
If you want to create a many-to-many relationship with EF Code-First, you should create another Entity
public class ContainerChildren
{
public int ElementContainerID { get; set; }
public List<ElementContainer> NestedContainers { get; set; }
}
this reference should help you to get the exact idea http://blogs.msdn.com/b/wriju/archive/2011/05/14/code-first-ef-4-1-building-many-to-many-relationship.aspx
Related
I have an entity in my database linked up with multiple entities and I need to store historical data for the changes (insert ,updates and delete) in the base entity as well as children entities.
Now the approach we are thinking of adopting is to keep every data in the corresponding history entity. The base table looks like this :
public partial class Con
{
public Guid Id { get; set; }
public string Note { get; set; }
...
public virtual ICollection<Document> Document { get; set; }
public virtual ICollection<ConLine> ConLine { get; set; }
public virtual ICollection<Leg> Leg { get; set; }
}
And the historical table looks like this, I am not sure about how to design the history table to hold linked tables data:
public partial class ConHistory
{
public Guid Id { get; set; }
public Guid ConId { get; set; }
public int TransactionId { get; set; }
...
public virtual ICollection<Document> Document { get; set; }
public virtual ICollection<ConLine> ConLine { get; set; }
public virtual ICollection<Leg> Leg { get; set; }
}
How do I approach this problem and What are the best industry practices? My main concern is when a child's data is being changed how do I log in to parent history table and the corresponding child history table.
For simple time-series data, keeping a separate table with a copy of the modifiable fields is a perfectly valid approach. Unfortunately, in your case you would also need to make a copy of each of the linked tables as well, so that you can maintain consistent foreign keys - e.g. DocumentHistory, ConLineHistory, LegHistory. It's a lot of repetitive code. And then you have to consider, what happens to all the historical records when the schema changes?
Personally, I would store this information as json, in a text column. All the fields that you search on should be in sql, so that you can index it, but the rest can be serialized to a json string:
public partial class ConHistory
{
public Guid Id { get; set; }
public Guid ConId { get; set; }
public int TransactionId { get; set; }
public Guid ModifiedByUser { get; set; }
public DateTime Date { get; set; }
// Serialize the rest of the `ConHistory` fields to a json object, and store them here
public string Json { get; set; }
}
Sql also has the JSON_VALUE function, and there are some examples of using this in Entity Framework, if you do need to get values out of the json string for querying.
I'm trying to implement hasthags into an application. I've configured the database already and even have a layout for how I'd like the form to look, however I'm not sure if it's possible to do what I want to do with Razor pages. I have the below classes:
public class Person
{
public int PersonId { get; set; }
public string FirstName { get; set; }
public string LastName{ get; set; }
public IList<PersonTag> PersonTags { get; set; }
}
public class Tag
{
public int TagId { get; set; }
public string TagName { get; set; }
public IList<PersonTag> PersonTags { get; set; }
}
public class PersonTag
{
public int PersonTagId { get; set; }
public int PersonId { get; set; }
public Person Person { get; set; }
public int TagId { get; set; }
public Tag Tag { get; set; }
}
And would like the form to look like this, where you see this input while editing a Person. You'd add a new hashtag by typing in the input box--hitting enter there (or pressing a button--not pictured) would create the tag in the Tag table and also create a new PersonTag relationship with the Person being edited, which would be saved on form submission. I guess the Tag could also get created on form submission if that's simpler. Clicking the "x" on one of the tags should also remove the PersonTag relationship
Is this something that's possible with razor pages? To this point I've only ever done simpler inputs (either single values or select lists), but in this case I need the user to have the option to enter free text multiple times. What kind of input would I need for these? Or would I need to do entirely special handling to pull the data on form submit, and just populate the tags with Javascript when the user adds them?
I'm using entity framework and I figured out that it ain't able to serialize the output of
EDM Objects. For now I'm using Northwind Products-table. SO thereforth I'm forced to cast the Object to another and are using the .Cast but it doesn't work.
The only solution I have is to property by property do it manually in my code, but I'm thinking - there must be a better way!
For god's sake - it is 2013! And this Entity seems like a good idea in the beginning but it has so many gotchas and constraints that it actually hinders more than it helps, but anyway the EDMX diagrams are nice!
Anybody who has a better solution to casting the objects?
POCO
public class Product
{
public int ProductID { get; set; }
public string ProductName { get; set; }
//public Nullable<int> SupplierID { get; set; }
//public Nullable<int> CategoryID { get; set; }
public string QuantityPerUnit { get; set; }
public Nullable<decimal> UnitPrice { get; set; }
public Nullable<short> UnitsInStock { get; set; }
public Nullable<short> UnitsOnOrder { get; set; }
public Nullable<short> ReorderLevel { get; set; }
//public bool Discontinued { get; set; }
public Category Category { get; set; }
//public ICollection<Order_Detail> Order_Details { get; set; }
//public Supplier Supplier { get; set; }
}
View Model
public class ProductsViewModel
{
public List<POCO.Product> Products { get; set; }
public ProductsViewModel()
{
using (NorthwindEntities dNorthwindEntities = new NorthwindEntities())
{
this.Products = dNorthwindEntities.Products.Cast<POCO.Product>().ToList();
Web api controller:
public class ProductsController : ApiController
{
public List<Product> GetAllProducts()
{
var viewmodel = new ProductsViewModel();
return viewmodel.Products;
}
1.
You can use frameworks like AutoMapper to handle Entities to ViewModel / DTO mapping automatically.
2.
Using Entities in the View (even in their POCO form) is not recommended for couple of reasons:
Security: Sending entities back to the client/view may expose more data than you intended.
Serialization: Since your entities usually contain reference to another entities and those entities may contain a reference back to the (parent) entity, you have to configure your serializer to handle this situation otherwise you'll get Circular Dependency Exception.
Incompatibility: The structure of your entity may not be compatible with what your view/client needs to render itself. Sometimes your view just needs a simple string while the entity holds this data in a much complex way hence the view needs to 'extract' it and you end up with a view full of unnecessary entity-drill-down code.
I have a datamodel like
ModelA which contains a Collection.
ModelB contains a Collection as a backreference. That is failing because of cyclic references if I query with Include("ModelB"). Not good but I solved that via setting ModelB.List=null for each element.
The problem now is submitting a changed ModelA tree: I am adding ModelB-entities to ModelA.ModelB[]. Now the UpdateEntity function is complaining the it could not add elements of type ModelB which are declared static. The JSON deserializer is creating static arrays.
How is it possible with the combination of upshot/MVC4 to submit datamodels which are not completely flat? As it is not possible right now to create your own DTO objects where you might figure out something I am stuck now...
After investigating the error a bit better, I think the problem is the cyclic backreference:
The ModelA->ModelB->ModelA is breaking the storage of the data. "Could not add data of type ModelA to type ModelB".
As I mentioned the backreference was set to Null because the cyclic ref serialisation problem...
I hope the will be some easier way on doing more manually with DTO objects where I have mroe control.
Please see also: MVC 4, Upshot entities cyclic references for the beginning of the journey...
To solve the cyclic backreference, you can use the ignoreDataMember attribute:
public class Customer
{
[Key]
public int CustomerId { get; set; }
public string Name { get; set; }
public string Address { get; set; }
public double Latitude { get; set; }
public double Longitude { get; set; }
public virtual ICollection<Delivery> Deliveries { get; set; }
}
public class Delivery
{
[Key]
public int DeliveryId { get; set; }
public string Description { get; set; }
public bool IsDelivered { get; set; }
[IgnoreDataMember]
public virtual Customer Customer { get; set; }
public virtual int CustomerId { get; set; }
}
I posted a working solution to your problem in a different question: https://stackoverflow.com/a/10010695/1226140
I'm having some trouble figuring out the appropriate FluentNHibernate mapping syntax for the following data model and domain objects. Here's the data model I'm working against:
And I'm trying to map the following domain objects to that model:
namespace FluentNHibernateSandbox.Entities
{
public abstract class EntityBase
{
public virtual long Id { get; set; }
}
}
namespace FluentNHibernateSandbox.Entities
{
public class Attribute : EntityBase
{
public virtual string Name { get; set; }
public virtual string Label { get; set; }
public virtual string Description { get; set; }
public virtual int SortOrder { get; set; }
public virtual Group Group { get; set; }
public virtual Editor Editor { get; set; }
}
}
namespace FluentNHibernateSandbox.Entities
{
public class Group : EntityBase
{
public virtual string Name { get; set; }
public virtual string Label { get; set; }
public virtual string Description { get; set; }
public virtual int SortOrder { get; set; }
public virtual IList<Attribute> Attributes { get; set; }
}
}
namespace FluentNHibernateSandbox.Entities
{
public class Editor : EntityBase
{
public virtual string ViewName { get; set; }
public virtual string WorkerClassName { get; set; }
}
}
In general, what I ultimately want doesn't seem like it should be all that hard to do, but I after having tried just about every combination of mappings I can think of, I still can't seem to get it right. I just need my Attribute to have a reference to the Group that it belongs to and a reference to the Editor assigned to it, and each Group should have a collection of the Attributes that are part of it. The couple of many-to-many join tables are what seem to be giving me fits. Particularly the APPLICATION_ATTRIBUTE table. Ultimately I only want the Attributes that my application is concerned with, in this case, those with an APPLICATION_ID of 4.
Any help would be greatly appreciated. Thanks.
Really kinda surprised nobody responded to this at all, but anyway. The answer/solution for this mapping situation that we came up with, which I was trying to avoid to start with, but turned out to really be the best way to go, was to create some custom views in the database that joined together all of the application-specific data I needed, and then just mapped my application's domain objects to those views. This worked at least partially because the information I needed from these tables is going to be read-only for this application, but even if I needed to write to the tables, I'm pretty sure (though haven't verified as I didn't really have need in this case) that I could have setup my views to be writeable and that would've worked too.
Hat tip to #robconery.