i'm writing a system to track observation values from sensors (e.g. temperature, wind direction and speed) at different sites. I'm writing it in C# (within VS2015) using a code-first approach. Although i've a reasonable amount of programming experience, I'm relatively new to C# and the code-first approach.
I've defined my classes as below. I've built a REST api to accept observation reading through Post, which has driven my desire to have Sensor keyed by a string rather than an integer - Some sensors have their own unique identifier built in. Otherwise, i'm trying to follow the Microsoft Contoso university example (instructors - courses- enrolments).
What I am trying to achieve is a page for a specific site with a list of the sensors at the site, and their readings. Eventually this page will present the data in graphical form. But for now, i'm just after the raw data.
public class Site
{
public int Id { get; set; }
public string Name { get; set; }
public ICollection<Sensor> Sensors { get; set; }
}
public class Sensor
{
[Key]
public string SensorName { get; set; }
public int SensorTypeId { get; set; }
public int SiteId { get; set; }
public ICollection<Observation> Observations { get; set; }
}
public class Observation
{
public int Id { get; set; }
public string SensorName { get; set; }
public float ObsValue { get; set; }
public DateTime ObsDateTime { get; set; }
}
and I've created a View Model for the page I'm going to use...
public class SiteDataViewModel
{
public Site Site { get; set; }
public IEnumerable<Sensor> Sensors { get; set;}
public IEnumerable<Observation> Observations { get; set; }
}
and then i try to join up the 3 classes into that View Model in the SiteController.cs...
public actionresult Details()
var viewModel.Site = _context.Sites
.Include(i => i.Sensors.select(c => c.Observations));
i used to get an error about "cannot convert lambda expression to type string", but then I included "using System.Data.Entity;" and the error has changed to two errors... on the 'include', I get "cannot resolve method 'include(lambda expression)'...". And on the 'select' i get "Icollection does not include a definition for select..."
There's probably all sorts of nastiness going on, but if someone could explain where the errors are (and more importantly why they are errors), then I'd be extremely grateful.
Simply you can you use like
viewModel.Site = _context.Sites
.Include("Sensors).Include("Sensors.Observations");
Hope this helps.
The way your ViewModel is setup, you're going to have 3 unrelated sets of data. Sites, sensors, and observations. Sites will have no inherent relation to sensors -- you'll have to manually match them on the foreign key. Realistically, your ViewModel should just be a list of Sites. You want to do
#Model.Sites[0].Sensors[0].Observations[0]
not something convoluted like
var site = #Model.Sites[0]; var sensor = #Model.Sensors.Where(s => SiteId == site.Id).Single(); etc...
Try doing
viewModel.Site = _context.Sites.Include("Sensors.Observations").ToList();
Eager-loading multiple levels of EF Relations can be accomplished in just one line.
One of the errors you reported receiving, by the way, is because you're using 'select' instead of 'Select'
And lastly, be aware that eager-loading like this can produce a huge amount of in-memory data. Consider splitting up your calls for each relation, such that you display a list of Sensors, and clicking, say, a dropdown will call an API that retrieves a list of Sites, etc. This is a bit more streamlined, and it prevents you from getting held up because your page is loading so much information.
Update
I've created a sample application for you that you can browse and look through. Data is populated in the Startup.Configure method, and retrieved in the About.cshtml.cs file and the About.cshtml page.. This produces this page, which is what you're looking for I believe.
Related
Let's say we have a realm results taken with
RealmDb.All<Entry>();
Then I want to do some search over those results using not yet supported techniques, like StartsWith on a function return or on a property which is not mapped in realm etc, so I get a subset
IEnumerable<Entry> subset = bgHaystack;
var results = subset.Where(entry => entry.Content.ToLower().StartsWith(needle));
To get somehow these as part of RealmResults, I extract the entry ids like this:
List<int> Ids = new List<int>();
foreach (Entry entry in entries)
{
Ids.Add(entry.Id);
}
return Ids;
and finally I want to return a subset of RealmResults (not IEnumerable) of only those Entries that contain those ids, how can I do that? IDE says the Contains method is not supported.
Can I use some kind of predicate or a comparer for that?
Entry is my model class
using System.ComponentModel.DataAnnotations.Schema;
using Realms;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;
using System;
namespace Data.Models
{
[Table("entry")]
public class Entry : RealmObject
{
public class EntryType
{
public const byte Word = 1;
public const byte Phrase = 2;
public const byte Text = 3;
};
[Key]
[PrimaryKey]
[Column("entry_id")]
public int Id { get; set; }
[Column("user_id")]
public int UserId { get; set; }
[Column("source_id")]
public int SourceId { get; set; }
[Indexed]
[Column("type")]
public byte Type { get; set; }
[Column("rate")]
public int Rate { get; set; }
[Column("created_at")]
public string CreatedAt { get; set; }
[Column("updated_at")]
public string UpdatedAt { get; set; }
[NotMapped]
public Phrase Phrase { get; set; }
[NotMapped]
public Word Word { get; set; }
[NotMapped]
public Text Text { get; set; }
[NotMapped]
public IList<Translation> Translations { get; }
[NotMapped]
public string Content
{
get {
switch (Type)
{
case EntryType.Phrase:
return Phrase?.Content;
case EntryType.Word:
return Word?.Content;
case EntryType.Text:
return Text?.Content;
}
return "";
}
}
}
}
According to the documentation, Realm .NET supports LINQ, so that's promising. In your specific example, you indicate that StartsWith isn't supported, but I see that on the above page, specifically here.
Now, your example makes clear that Entry is a RealmObject, so it's not clear where you'd possibly get a RealmResult from (nor does their documentation on that page mention a RealmResult). Specifically, the home page indicates that you're really only going to ever work with Realm, RealmObject and Transaction, so I'm going to just assume that you meant that you'll need a resulting RealmObject per their examples.
The way you presently have your data object set up, you're rather stuck calling it like you are (though if I could make a recommendation to simplify it a little bit:
var entries = RealmDb.All<Entry>().ToList();
var results = entries.Where(entry => entry.Content.ToLower().StartsWith(needle));
var ids = results.Select(a => a.Id).ToList();
Now, your big issue with just combining the filter predicate in line 2 with the end of line 1: Content itself is marked with a [NotMapped] attribute. Per the documentation again:
As a general rule, you can only create predicates with conditions that
rely on data in Realm. Imagine a class
class Person : RealmObject
{
// Persisted properties
public string FirstName { get; set; }
public string LastName { get; set; }
// Non-persisted property
public string FullName => FirstName + " " + LastName;
}
Given this class, you can create queries with conditions that apply to
the FirstName and LastName properties but not to the FullName
property. Likewise, properties with the [Ignored] attribute cannot be
used.
Because you're using [NotMapped], I've got to believe that's going to behave similarly to [Ignored] and further, because it's just a computed value, it's not something that Realm is going to be able to process as part of the query - it simply doesn't know it because you didn't map it to the information Realm is storing. Rather, you'll have to compute the Content property when you've actually got the instances of your Entry objects to enumerate through.
Similarly, I expect you'll have issues pulling values from Phrase, Word and Text since they're also not mapped, and thus not stored in the record within Realm (unless you're populating those in code you didn't post before executing your Where filter).
As such, you might instead consider storing separate records as a PhraseEntry, WordEntry, and TextEntry so you can indeed perform exactly that filter and execute it on Realm. What if you instead used the following?
public class Entry : RealmObject
{
[Key]
[PrimaryKey]
[Column("entry_id")]
public int Id { get; set; }
[Column("user_id")]
public int UserId { get; set; }
[Column("source_id")]
public int SourceId { get; set; }
[Column("rate")]
public int Rate { get; set; }
[Column("created_at")]
public string CreatedAt { get; set; }
[Column("updated_at")]
public string UpdatedAt { get; set; }
[Column("content")]
public string Content { get; set; }
[NotMapped]
public IList<Translation> Translations { get; }
}
[Table("wordEntry")]
public class WordEntry : Entry
{
}
[Table("phraseEntry")]
public class PhraseEntry : Entry
{
}
[Table("textEntry")]
public class TextEntry : Entry
{
}
And now, you can offload the filtering to Realm:
var wordEntries = RealmDb.All<WordEntry>.Where(entry =>
entry.Content.StartsWith(needle, StringComparison.OrdinalIgnoreCase)).ToList();
var phraseEntries = RealmDb.All<PhraseEntry>.Where(entry => entry.Content.StartsWith(needle, StringComparison.OrdinalIgnoreCase)).ToList();
var textEntries = RealmDb.All<TextEntry>.Where(entry => entry.Content.StartsWith(needle, StringComparison.OrdinalIgnoreCase)).ToList();
var entries = new List<Entry>();
entries.AddRange(wordEntries);
entries.AddRange(phraseEntries);
entries.AddRange(textEntries);
var ids = entries.Select(entry => entry.Id).ToList();
It's not quite as brief as storing it all in one table, but I'm not immediately seeing any Realm documentation that indicates support for executing the same query against multiple tables simultaneously, so at least this would allow you to leave the filtering to the database and work against a more limited subset of values locally.
Finally, so we have all that and I missed your final question up top. You indicate that you want to return a subset of your entries based on some collection of ids you create. In the logic you provide, you're retrieving all the Id properties in all your results, so there's really no further subset to pull.
That said, let's assume you have a separate list of ids that for whatever complicated reason, you were only able to derive after retrieving the list of Entry types from above (themselves all PhraseEntry, WordEntry or TextEntry objects).
At this point, since you've already pulled all the values from Realm and have them locally, just execute another Where statement against them. Because a List implements IEnumerable, you can thus execute the LINQ locally without any of the Realm restrictions:
var myLimitedIdSet = new List<int>()
{
10, 15, 20, 25 //Really complicated logic to narrow these down locally
};
var resultingEntries = entries.Where(entry => myLimitedIdSet.Contains(entry.Id)).ToList();
And you're set. You'll have only those entries that match the IDs listed in myLimitedIdSet.
Edit to address comment
You see this error because of the detail provided at the top of this page in the documentation. Specifically (and adapting to your code):
The first statement gives you a new instance of Entry of a class that implements IQueryable... This is standard LINQ implementation - you get an object representing the query. The query doesn't do anything until you made a further call that needs to iterate or count the results.
Your error is then derived by taking the result from RealmDb.All<Entry>() and trying to cast it to an IEnumerable<Entry> to operate against it as though you have local data. Until you call ToList() onRealmDb.All` you simply have a LINQ representation of what the call will be, not the data itself. As such, when you further refine your results with a Where statement, you're actually adding that to a narrowed version of the IQueryable statement, which will also fail because you lack the appropriate mapping in the Realm dataset.
To skip the optimization I provided above, the following should resolve your issue here:
var bgHaystack = realm.All<Entry>().ToList(); //Now you have local data
var results = bgHaystack.Where(entry => entry.Content.ToLower().StartsWith(needle));
Unfortunately, given your provided code, I don't expect that you'll see any matches here unless needle is an empty string. Not only is your Content property not part of the Realm data and you thus cannot filter on it within Realm, but neither are your Phrase, Word or Text properties mapped either. As a result, you will only ever see an empty string when getting your Content value.
You can further refine the results variable above to yield only those instances with a provided ID as you see fit with normal LINQ (as again, you'll have pulled the data from Realm in the first line).
var limitedIds = new List<int>{10, 20, 30};
var resultsLimitedById = results.Select(a => limitedIds.Contains(a.Id)).ToList();
I've updated my examples above to reflect the use of ToList() in the appropriate places as well.
I am very new to asp.net and C# so bear with me. I am trying to return data from a database using the entity framework .include() method so that I can get the foreign key information from another table. However, what is being returned is only part of the data. It seems to be cut off before everything is returned.
"[{"id":11,"name":"Mr. Not-so-Nice","heroType":3,"heroTypeNavigation":{"id":3,"type":"Villian","heroes":["
Which gives me the error: SyntaxError: Unexpected end of JSON input.
Please seem below for the model classes and the GET section of the controller where this is being returned. If I remove the "include()" method it returns all the heroes from the main table just fine.
public partial class Hero
{
public int Id { get; set; }
public string Name { get; set; }
public int? HeroType { get; set; }
public virtual HeroTypes HeroTypeNavigation { get; set; }
}
{
public partial class HeroTypes
{
public HeroTypes()
{
Heroes = new HashSet<Hero>();
}
public int Id { get; set; }
public string Type { get; set; }
public virtual ICollection<Hero> Heroes { get; set; }
}
// GET: api/Heroes
[HttpGet]
public async Task<ActionResult<IEnumerable<Hero>>> GetHeroesTable()
{
return await _context.HeroesTable.Include(hero => hero.HeroTypeNavigation).ToListAsync();
}
Serializer recursion rules will be tripping this up. Basically as jonsca mentions, you have a circular reference between hero, and hero type. The serializer will start with the hero, then go to serialize the hero type which it will find the Hero's collection and expect to serialize, which each would reference a hero type, with collections of Heros.. The serializer bails when it sees this.
I would recommend avoiding passing back Entity classes to your view to avoid issues with EF and lazy loading. Serialization will iterate over properties, and this will trigger lazy loads. To avoid this, construct a view model for the details your view needs, flatten as necessary.
For example if you want to display a list of Heroes with their Type:
public class HeroViewModel
{
public int HeroId { get; set; }
public string Name { get; set; }
public string HeroType { get; set; }
}
to load:
var heroes = await _context.HeroesTable.Select(x => new HeroViewModel
{
HeroId = x.HeroId,
Name = x.Name,
HeroType = x.HeroType.Type
}).ToListAsync();
You can utilize Automapper for example to help translate entities to view models without that explicit code using ProjectTo<TEntity> which can work with EF's IQueryable implementation.
With larger realistic domains your client likely won't need everything in the object graph.
You won't expose more information than you need to. (I.e. visible via debugging tools)
You'll get a performance boost from not loading the entire graph or triggering
lazy load calls, and it's less data across the wire.
The last point is a rather important one as with complex object graphs, SQL can do a lot of the lifting resulting in a much more efficient query than loading "everything". Lazy hits to the database can easily add several seconds to each and every call from a client, and loading large graphs has a memory implication on the servers as well.
I am working on a service oriented architecture. I have 3 tables Meeting, Stakeholder and MeetingStakeholder (a junction table).
A simple representation of POCO classes for all 3 tables:
public class Meeting
{
public int Id { get; set; }
public IList<MeetingStakeholder> MeetingStakeholders { get; set; }
}
public class Stakeholder
{
public int Id { get; set; }
}
public class MeetingStakeholder
{
public int Id { get; set; }
public int MeetingId { get; set; }
public Meeting Meeting { get; set; }
public int StakeholderId { get; set; }
public Stakeholder Stakeholder { get; set; }
}
A simple representation of Meeting Dto:
public class MeetingDto
{
public int Id { get; set; }
public IList<int> StakeholderIds { get; set; }
}
In PUT action,
PUT: api/meetings/1
First I removes all existing records from MeetingStakeholder (junction table) then prepares new List<MeetingStakeholder> meetingStakeholders using meetingDto.StakeholderIds and create it.
{
List<MeetingStakeholder> existingMeetingStakeholders = _unitOfWork.MeetingStakeholderRepository.Where(x=> x.MeetingId == meetingDto.Id);
_unitOfWork.MeetingStakeholderRepository.RemoveRange(existingMeetingStakeholders);
List<MeetingStakeholder> meetingStakeholders = ... ;
_unitOfWork.MeetingRepository.Update(meeting);
_unitOfWork.MeetingStakeholderRepository.CreateRange(meetingStakeholders);
_unitOfWork.SaveChanges();
return OK(meetingDto);
}
Everything is fine to me. But my architect told me that i am doing wrong thing.
He said, in PUT action (according to SRP) I should not be removing and re-creating MeetingStakeholder records, I should be responsible for updating meeting object only.
According to him, MeetingStakeholderIds (array of integers) should be send in request body to these routes.
For assigning new stakeholders to meeting.
POST: api/meetings/1/stakeholders
For removing existing stakeholders from meeting.
Delete: api/meetings/1/stakeholders
But the problem is, In meeting edit screen my front-end developer uses multi-select for Stakeholders. He will need to maintain two Arrays of integers.
First Array for those stakeholders Ids which end-user unselect from multi-select.
Second Array for new newly selected stakeholders Ids.
Then he will send these two arrays to their respective routes as I mentioned above.
If my architect is right then I have no problem but how should my front-end developer handle stakeholders selection in edit screen?
One thing I want to clarify that my junction table is very simple, it does not contain additional columns other than MeetingId and StakeholderId ( a very basic junction). So in this scenario, does it make sense to create separate POST/DELETE actions on "api/meetings/1/stakeholders" that receives StakeholderIds (list of integers) instead of receiving StakeholderIds directly in MeetingDto??
First of all, if I am not mistaken:
you have a resource: "Meeting";
you want to update the said resource (using HTTP/PUT).
So updating a meeting by requesting a PUT on "/api/meetings/:id" seems fairly simple, concise, direct and clear. All good traits for designing a good interface. And it still respects the Single Responsibility Principle: You are updating a resource"
Nonetheless, I also agree with you architect in providing, in addition to the previous method, POST/Delete actions on "api/meetings/1/stakeholders" if the requisites justify so. We should be pragmatic at some level not to overengineer something that isn't required to.
Now if your architect just said that because of HOW IT IS PERSISTED, then he is wrong. Interfaces should be clear to the end user (frontend today, another service or app tomorrow ...), but most importantly, in this case, ignorant of its persistence or any implementation for that matter.
Your api should focus on your domain and your business rules, not on how you store the information.
This is just my view. If someone does not agree with me I would like to be called out and so both could grow and learn together.
:) Hope I Could be of some help. Cheers
I'm developing a web app that contains a User entity that is derived from .NET Core's IdentityUser. Lets suppose there is another entity called Comment which has a relation to a user (the user who posted the comment):
public class User : IdentityUser
{
public string SomeExtraField { get; set; }
}
public class Comment
{
//Owner (Creator) of the feedback
public User User { get; set; }
//body of the comment
public string Body { get; set; }
}
Now suppose I have an API endpoint that returns all of the comments in the system. If I query for all comments and include the User relation, when the object gets serialized, everything in the User class is serialized and sent to the client (including the users hashed password, etc). Obviously I don't want this. So I've created a CommentService layer that grabs the Comments from a CommentRepository. From my understanding, the service layer should do the job of mapping the raw Comment object into a Comment DTO, which only contains data that should be sent to the client. I've defined a comment and user DTO like this:
public class UserOutput
{
public string Id { get; set; }
public string SomeExtraField { get; set; }
}
public class CommentOutput
{
public UserOutput User { get; set; }
public string Body { get; set; }
}
Then in my service layer I have something like the following:
//Fetch all comments
var list = await _repository.ListAsync();
//Map comments to DTO
var result = list.Select(x => new CommentOutput
{
Body = x.Body,
User = new UserOutput
{
Id = x.User.Id,
SomeExtraField = x.User.SomeExtraField,
}
});
This all seems to work great. However I can foresee one problem. Lets say I have a large system with Comments, Posts, Likes, Private Messages, etc. I can map them all in a similar fashion above. Then one day I decide to add another field to the UserOutput DTO. Now I have to go through potentially hundreds of mapping code like the sample above to map the new field properly, and whats worse is the compiler wont tell me if I've missed anything. I would like to have a function somewhere that maps a User to a UserOutput but I don't know where it should go.
I've seen some suggestions to put a constructor to the DTO that does the mapping:
public class UserOutput
{
public UserOutput(User user)
{
Id = user.Id;
SomeExtraField = user.SomeExtraField
}
public string Id { get; set; }
public string SomeExtraField { get; set; }
}
but I've seen people against this because it tightly couples the DTO with the Entity. I've also seen suggestions of using Auto Mapper but is also seems an equal amount of people are against it.
Where should I place code that can perform these DTO->entity and entity->DTO mappings so I don't repeat myself all over the place?
Try to check out AutoMapper.
This library will help you to map the Entity Class into the ViewModel.
The way to use it is pretty straightforward.
This is the 3rd major edit to this question, so I'm going to write a quick little summary first, then ask the question.
I have an input/edit model I'm planning on using with an EF4-backed MVC 2 site. The model is as follows:
public class AdminGameEditModel
{
[Required]
public int GameID { get; set; }
[Required(ErrorMessage="A game must have a title")]
public string GameTitle { get; set; }
[Required(ErrorMessage="A short URL must be supplied")]
public string ShortURL { get; set; }
[Required(ErrorMessage="A box art image must be supplied")]
public HttpPostedFileBase BoxArt { get; set; }
[Required(ErrorMessage="A large image for the index page is required")]
public HttpPostedFileBase IndexImage { get; set; }
[Required(ErrorMessage="A game must have a review")]
public string ReviewText { get; set; }
[Required(ErrorMessage="A game must have a score")]
public int ReviewScore { get; set; }
[Required(ErrorMessage="A game must have at least one Pro listed")]
public string[] Pros { get; set; }
[Required(ErrorMessage="A game must have at least one Con listed")]
public string[] Cons { get; set; }
[Required(ErrorMessage="A game must belong to a genre")]
public int GenreID { get; set; }
[Required(ErrorMessage="A game must be associated with at least one platform")]
public int[] PlatformIDs { get; set; }
}
I'd like to map it to a Game entity for creation/updating. There's a snag, though - I need to save the images in a particular folder, and then take their paths and save those as properties in my entity. So, an example for clarity's sake: rather than my Game entity having a actual BoxArt image, it would instead have the path to the correct BoxArt image. I hope this makes sense. Let me know if I need to clarify.
Can I do this with AutoMapper? If so, can anyone provide some code guidance?
EDIT:
Part of the problem is that my model is fairly complex, as it contains a many-to-many relationship. The PlatformIDs are ultimately used to build/rebuild (depending whether I'm creating or updating an entity) linked Platform entities in the Game/Platform map. I'm not sure if AutoMapper can do something that complex without needing to go through my repository.
Then there's the problem of the image paths. The paths aren't a property of HttpPostedFileBase, but must be constructed by hand like so:
if (BoxArt.ContentLength > 0) {
var fileName = Path.GetFileName(BoxArt.FileName);
var path = Path.Combine(Server.MapPath("~/Content/Images/BoxArt"), fileName);
BoxArt.SaveAs(path);
}
So, what I'm looking for is more complex than just trying to map simple properties across objects. I'd like to keep a reference to my edit model out of my repository. Separation of concerns, and all that. Because of that, I need to map to an entity before I attempt to pass it to my repo for saving. I'm just not sure how to do it without blending app layers.
If I understand you, all you need to do is update your properties first prior to the call to AutoMapper.
Make sure your object has the correct values prior to calling AutoMapper.
After the call to do the mapping, your destination object will have all the matching properties copied over.
Post some more code if this doesn't answer the questoin.