I have a table in my database, where I put states of USA (just ID and state name).
I want to get these values in my controler - shall I do standard operations: add context in my EF, later get objects? Or there is another way to get it?
I don't want to make any changes in this table, so db.XYZ.Add, db.XYZ.SaveChanges() etc. methods is not important for me.
What is the best practise to get objects like "states" or for example base of "zip codes"?
Later, second question: what means "virtual" in code like this:
[Table("Users")]
public class User
{
(..)
public virtual string UserType { get; set; }
Regards!
Entity framework allows getting objects from the database without adding them to the change tracker:
using (var db = new MyContext())
{
var states = db.States.AsNoTracking();
...
}
However, when you use a State object in a reference, e.g. like:
var address = new Address() { State = state1 };
db.Addresses.Add(address);
db.SaveChanges();
where state1 is a State object, state1 will be attached to the context after all and have EntityState.Added!
So you should still be careful how to use these "untracked" objects. In this example you'd better set a primitive StateId property:
var address = new Address() { StateId = state1.Id };
(does not attach state1).
What you'd really want in this case is preventing EF from ever changing the EntityState of a State object. There is no way I can think of to enforce this. Would be an interesting feature.
what means "virtual" in code like this
The virtual modifier is commonly used to enable lazy loading of navigation properties. Address could have
public virtual State State { get; set; }
Now when you grab an address from the database and afterwards access its State property, the state is loaded from the database at that moment. This is because under the hood EF creates an Address object that is a derivative of your Address class and that has overridden the State property with code that enables lazy loading.
However, in the code you show virtual has no bearing on lazy loading because it is a string property. So it can't be a navigation property and it does not allow lazy loading.
In code first I use an enums to save items with an int id and description.
To do it this way I add the following:
In the user add:
...
public int StateId { get; set; }
public State State
{
get { return (State)StateId ; }
}
...
Create an enum:
public enum State
{
State1,
State2
}
The enum Id is saved back as a StateId to the User each time I save a user.
On this link you can find more about "virtual" in your code
To get all states you can easy do this:
var getStates = from i in db.States select i;
and of course you can add some conditions if you want.
Related
I am using the Neo4j .Net client to interface with a Neo4j database.
I often come by this issue when trying to map related nodes to nested classes :
For example mapping
(:Foo)-[:FOOBAR]->(:Bar)
to the form
public class Foo {
public string FooPropOne { get; set; }
public string FooPropTwo { get; set; }
public List<Bar> Bars { get; set; }
}
public class Bar {
public string BarPropOne { get; set; }
public string BarPropTwo { get; set; }
}
To get the correct output for deserialzation I have to write the query like so:
Foo foo = WebApiConfig.GraphClient.Cypher
.Match("(f:Foo)-[:FOOBAR]->(b:Bar)")
.With("#{
FooPropOne: f.FooPropOne,
FooPropTwo: f.FooPropTwo,
Bars: collect(b)
} AS Result")
.Return<Foo>("Result")
.SingleOrDefault();
To a certain extent this is fine, and works perfectly, but becomes quite unwieldy the more properties the Foo class has.
I was wondering if there was something I can do in the "With" statement to add a temporary property (in the above case "Bars") when returning the nodes, that does not require me to write every single property on the parent node?
Something like
.With("f.Bars = collect(b)")
.Return<Foo>("f")
that wont actually affect the data stored in the DB?
Thanks in advance for any relpies!!
I don't know of a way to add a temporary property like you want, personally - I would take one of two approaches, and the decision really comes down to what you like to do.
Option 1
The choosing properties version
var foo = client.Cypher
.Match("(f:Foo)-[:FOOBAR]->(b:Bar)")
.With("f, collect(b) as bars")
.Return((f, bars) => new Foo
{
FooPropOne = f.As<Foo>().FooPropOne,
FooPropTwo = f.As<Foo>().FooPropTwo,
Bars = Return.As<List<Bar>>("bars")
}).Results.SingleOrDefault();
This version allows you to be Type Safe with your objects you're bringing out, which on a class with lots of properties does limit the chance of a typo creeping in. This will give you back a Foo instance, so no need to do any other processing.
Option 2
The little bit of post-processing required version
var notQuiteFoo = client.Cypher
.Match("(f:Foo)-[:FOOBAR]->(b:Bar)")
.With("f, collect(b) as bars")
.Return((f, bars) => new
{
Foo = f.As<Foo>(),
Bars = bars.As<List<Bar>>()
}).Results;
This saves on the typing out of the properties, so in a big class, a time saver, and also means if you add extra properties you don't need to remember to update the query. However you do need to do some post-query processing, something like:
IEnumerable<Foo> foos = notQuiteFoo.Results.Select(r => {r.Foo.Bars = r.Bars; return r.Foo;});
Personally - I like Option 2 as it has less potential for Typos, though I appreciate neither is exactly what you're after.
I wish to give a Person as defined below, the ability to print a vCard out of my system. To provide the user with privacy options, the user can select whether to show/hide certain properties. In it's simplest form, I need to have a separate table that would hold the user's choices.
I was wondering if it was possible to build this configurator table using reflection. As shown in the Person model below, I could decorate properties with a custom attribute, and then using those properties, construct and persist a model that would have a bool property for every decorated Person property.
public class Person
{
public string UserName { get; set; }
public string FirstName { get; set; }
[DisplayOnVCard]
public string LastName { get; set; }
[DisplayOnVCard]
public string Email { get; set; }
[DisplayOnVCard]
public string MobilePhone { get; set; }
}
** where [DisplayOnVCard] is a custom attribute.*
At the end of this, I expect a table in the db that would correspond to this:
public class VCardConfigurator
{
public bool LastName { get; set; }
public bool Email { get; set; }
public bool MobilePhone { get; set; }
}
This is just a sample representation of what is actually a huge entity. Which is why I hope to avoid manually mapping a bool field to each optional property.
I believe this problem domain is quite similar to how, for instance, privacy settings work on social networking sites, yes?
While I was typing this, I did ponder upon the possibility that if down the line I was to remove the attribute from one of the properties, what implications that might have. Needs some thought!
Further reading for self:
Programmatically adding properties to an MVC model at runtime
There is a huge possibility that I am galloping down a totally wrong path! If that is the case, please advice so!
#1 Update
I am not sure its possible to add or remove attributes for an instance since attributes are at the class level, but their property values can be changed (Since they are instances).
My suggested solusion
I am not sure what you mean in "I expect a table in the db that would correspond to this",
since you can't have a table in the database that contains only the columns of the non-privacy properties for each user.
You will need a dedicated table for this mapping (Lets say 'PrivacyMappings' table), with these columns:
UserId, PropertyName, IsPrivate.
When a user is added, all the properties will be added to this table with a default privacy settings (for instance, all properties are non-private by default).
You can add the properties by iterating over them and insert them as you said.
You can use the following class in entity framework:
public class PrivacyMapping
{
public int UserId {get;set;}
public string PropertyName {get;set;}
public bool IsPrivate {get;set;}
}
Adding the default privacy settings when a user being added:
// retrieve user model properties.
foreach (property in properties)
{
//iterrate over the user Properties.
context.PrivacyMapping.Add(new PrivacyMapping(user.userId, propertyName, isPrivate);
}
context.SaveChanges()
Now you can take all the user non-private properties by
context.PrivacyMapping.Where(p=>p.UserId == user.id && !IsPrivate).Select(p=>p.PropertyName);
And now you can deal with information any way you want.
For example, you can have a VCardItems class, that receive an user id/object in its c'tor and stores a dictionary of the allowed properties by their names.
public class VCardItems{
private Dictionary<string, object> properties{get;set;}
public VCardItems(User user)
{
// initiate values..
}
public object this[string name] {
get
{
if (properties.ContainsKey(name))
{
return properties[name];
}
// A private property.
return null;
}
set
{
properties[name] = value;
}
}
}
There is other options of how to use the data, for example with ActionFilter that in this case sets the private properties to null or storing the non-private data in the HttpContext.Items dictionary,
but it really up to you.
First message
Before we get into details, I wonder how you expect to use this class.
If a view (or whatever going to handle it), going to receive have a runtime-generated class for example, how you gonna handle it?
How you gonna know what properties this model has?
There is a field in our database which really ought to be a boolean, but for some reason the original developers made it a CHAR which will either be set to "1" or "0".
[Column("CHARGEABLE")]
[StringLength(1)]
private string Chargeable { get; set; }
I want my model to represent this field as a boolean so I figured I could add a property to my model to wrap it:
[NotMapped]
public bool ChargeableTrue
{
get
{
return Chargeable == "1" ? true : false;
}
set
{
Chargeable = value ? "1" : "0";
}
}
Now on my View I just display the EditorFor ( ChargeableTrue ), but when I click save it doesn't actually update it.
I think what is happening is that when the model is being updated, it's still attempting to get the value of 'Chargeable' from the View, even though I haven't displayed it there. And since there is no input field, it just gets null and ends up saving that to the database.
if (ModelState.IsValid)
{
db.Entry(call).State = EntityState.Modified;
db.SaveChanges();
return RedirectToAction("Index");
}
What is one expected to do in this situation?
Based on KMan's answer, here's the extended version just in case you're not familiar with creating view models.
The idea is that your domain object is not really what you want to be updating exactly from your views. Instead, you create a go-between that can also include view-specific items (like a list of objects to populate a drop-down).
public class MyViewModel {
public bool Chargeable { get; set; }
}
Now you can do this:
#* In view *#
Html.EditorFor(m => m.Chargeable)
// In controller
public ActionResult Save(MyViewModel model) {
if (ModelState.IsValid) {
var domainObject = new MyObject() {
Chargeable = model.Chargeable ? "1" : "0"
};
// the rest of your code using domainObject
}
}
I'd consider just creating an overload of your domain object's constructor that accepts your view model to keep the mapping in one place. I typically use a tool like AutoMapper to map objects or manual extension methods.
A view model typically contains a sub-set of your domain object's properties, but can contain all of them or more properties like lists, visbility states, etc. They come in incredibly useful and I've never done a MVC project where I haven't used them.
Use a view model and make your mapping on the controller.
I am working on asp.net MVC 3 application and I am using codeFirst approach. I am trying to create history table or user table, Where I want to keep track of what columns were modified by user. How can I do this using EF Code First.
Do I need to do it after DataContext.savechanges ?
Please suggest.
Thanks.
The DbContext has a method called Entry<T>:
var entity = context.Items.Find(id);
entity.Name = "foobar";
var entry = context.Entry<Item>(entity);
entry will be of type DbEntityEntry<T> and has the properties OriginalValues and CurrentValues.
You could probably write something that will generically inspect these properties to see what has changed and then automatically insert a new record into your history table.
Either that, or use database triggers.
I'm not sure if this is really the "appropiate" way to do it, but this is how its usually done in sql:
Create an extra property version of type int or something.
Because you probably do not want to loop every time, add another property IsLatestVersion of type bool
When an entity is saved, check if the entity already exists. If so, set the entity on IsLatestVersion = false.
Increment the version, and save the changes as new entity.
Sounds to me like you want an a filter that inherits from ActionFilterAttribute. In my case, this is the simplest example that I have. This is my model, notice that the attributes dictate the mapping to the database.
[Table("UserProfile")]
public class UserProfile
{
[Key, DatabaseGeneratedAttribute(DatabaseGeneratedOption.Identity)]
public int UserId { get; set; }
public string UserName { get; set; }
}
In my case, it was as simple as the following, although it was not historical:
public sealed class UsersContext : DbContext
{
public UsersContext() : base("DefaultConnection")
{
}
public DbSet<UserProfile> UserProfiles { get; set; }
}
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
LazyInitializer.EnsureInitialized(ref _initializer, ref isInitialized, ref initializerLock);
}
public void CheckDatabase()
{
Database.SetInitializer<YourDBContextType>(null);
using (var context = new YourDBContextType())
{
if (!context.Database.Exists())
{
((IObjectContextAdapter)context).ObjectContext.CreateDatabase();
}
}
// Uses your connection string to build the following table.
WebSecurity.InitializeDatabaseConnection("DefaultConnection", "UserProfile", "UserId", "UserName", autoCreateTables: true);
}
The end result is not only EF being code first, but also allows for your models for your views to use primitives derived from your complex entities. Now, if you have another, lets say historical, DBContext then I would recommend modifying either the text transformation file or creating a base class for your entities. Both ways allow for an easy generation of code that could insert into your table, then follow up with that entity, clone it into a historical model and save. All that being said, I am a fan of database first approaches with concentration on constraints, triggers, etc. instead of a framework.
I have built a simple MVC3-based ticket entry site for a less-than-usable call center application and am attempting to refactor my prototype to better adhere to design patterns partly to make it more maintainable going forward but mostly as a learning exercise.
The user-facing view is a form consisting of basic user information in addition to a few panels allowing selection of various resource types. Each resource type (hardware, software, etc) is displayed in the same way: using dual, filterable listboxes with add/remove buttons, an optional “justification” textarea that conditionally displays if a requested resource requires justification, and general comments.
I have built the following ViewModel for the individual panels:
public class RequestableList
{
// list of requestable items ids requiring justification
private List<string> _restrictedItems = new List<string>();
public List<string> RestrictedItems
{
get { return _restrictedItems; }
set { _restrictedItems = value; }
}
// the key-value pairs from which to populate available items list
private Dictionary<string, string> _availableItems = new Dictionary<string, string>();
public Dictionary<string, string> AvailableItems
{
get { return _availableItems; }
set { _availableItems = value; }
}
// item ids requested by user
private List<string> _requestedItems = new List<string>();
public List<string> RequestedItems
{
get { return _requestedItems; }
set { _requestedItems = value; }
}
}
The main ViewModel is then comprised of multiple RequestableLists as necessary:
public class SimpleRequestViewModel
{
public UserInfo userInfo { get; set; }
public RequestableList Software {get;set;}
public RequestableList Hardware {get;set;}
public RequestableList Access {get;set;}
public string SoftwareAdditionalInfo { get; set; }
public string HardwareAdditionalInfo { get; set; }
public string AccessFileMailShare { get; set; }
public string AccessAdditionalInfo { get; set; }
public string SoftwareJustification { get; set; }
public string HardwareJustification { get; set; }
public string AccessJustification { get; set; }
public string Comment { get; set; }
}
I have created a strongly typed view for SimpleRequestViewModel (and its variant) and a strongly typed EditorTemplate for RequestableList that wires up the dual listboxes, filtering, and jquery. All renders well and is working but the code currently smells.
When posting to the controller, if the model is valid I must translate it into a readable text description in order to create a new ticket in in the call center app. It doesn’t feel right to have the controller performing that translation into readable text but I run into hurdles when trying to design another class to translate the viewmodels.
Only the selected item values are posted so before translating the request into text I must first lookup the appropriate text for the provided values (they are required in description). The controller is currently the only object that has access to the call center data model for this lookup query.
There are 2 similar ViewModels containing varying combinations of RequestableLists so any translator must be able to translate the various combinations. One has only Hardware and Software, another may have Hardware Software, and a few more RequestableLists.
I considered overriding ToString() directly in the ViewModel but didn’t like that business logic (conditional rendering) there, and again, once posted, the ViewModel doesn’t contain the text for the selected items in the listbox so it would need access to the data model.
The translation of posted values to text as it is currently handled in the controller smells as it’s handled in a switch statement. The controller takes each posted RequestableList and populates the original “Available” fields before it builds the new ticket description.
switch (requestCategory)
{
case RequestableCategory.Software:
itemList = sde.GetSoftware();
break;
case RequestableCategory.Hardware:
itemList = sde.GetHardware();
break;
case RequestableCategory.Access:
itemList = sde.GetAccess();
break;
case RequestableCategory.Telecom:
itemList = sde.GetTelecom();
break;
default:
throw new ArgumentException();
}
So, my question(s):
What patterns are techniques would you recommend for performing the posted viewmodel to ticket description translation?
How do you typically handle the “only posts value” issue with select boxes when you need the text as well as the value?
Is there a better way for me to be approaching this problem?
Again, I am hoping this is a learning experience for me and am more than willing to provide additional information or description if needed.
A few suggestions:
Abstract the logic that does the call center submission into its own class. Provide (from the controller) whatever dependencies it needs to access the call center DB. Have different methods to handle the various types of view models using overloading. Presumably the descriptions come from the DB so you can extract the description from the DB based on the value in this class. This class could also take responsibility for building your view models for the display actions as well. Note that with this pattern the class can interact with the DB directly, through a repository, or even via web services/an API.
Use a repository pattern that implements some caching if performance is an issue in looking up the description from the DB the second time. I suspect it won't be unless your call center is very large, but that would be the place to optimize the query logic. The repository can be the thing that the controller passes to the submission class.
If you don't need to access the DB directly in the controller, consider passing the broker class as a dependency directly.
It might look like:
private ICallCenterBroker CallCenterBroker { get; set; }
public RequestController( ICallCenterBroker broker )
{
this.CallCenterBroker = broker;
// if not using DI, instantiate a new one
// this.CallCenterBroker = broker ?? new CallCenterBroker( new CallCenterRepository() );
}
[HttpGet]
public ActionResult CreateSimple()
{
var model = this.CallCenterBroker.CreateSimpleModel( this.User.Identity.Name );
return View( model );
}
[HttpPost]
public ActionResult CreateSimple( SimpleRequestViewModel request )
{
if (Model.IsValid)
{
var ticket = this.CallCenterBroker.CreateTicket( request );
// do something with ticket, perhaps create a different model for display?
this.CallCenterBroker.SubmitTicket( ticket );
return RedirectToAction( "index" ); // list all requests?
}
return View();
}