I recently started a project with MongoDB in C#. Im starting to learn the basics about it but today I walked into a problem which I cant seem to figure out. Im having an OrderBy() method on my collection with Linq. Im trying to order the collections based on an IF statement using the $cond aggregate function. However I get an error which says:
only fields are allowed in a $sort
Basically Ive tried anything I could find. The solution right now is to turn the IQueryable into a list, then follow up by ordering that list. But I want to order it by the server to save performance.
Right now Im calling the query and trying to order it as I said before.
This is the code that gives the error.
var query = collection.AsQueryable().Where(x => x.ReportId == 1).OrderBy(x => x.Origin == 0 ? "Test 1" : "Test 2" );
foreach(var item in query){
Console.WriteLine(item.Name);
}
x reassembles the following class
public ObjectId _id { get; set; }
public int ReportId { get; set; }
public int RecId { get; set; }
public int Origin { get; set; }
public string Name { get; set; }
Whenever I try to loop through it I get the error: only fields are allowed in a $sort
I basically want to execute the query ordered by the result inside the IF.
Right now it gets stuck when trying to execute the query.
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 writing an APS.NET MVC 5 application. I am stuck with small issue that I am not actually able to figure out.
I am getting error as follows:
System.ArgumentOutOfRangeException: 'Index was out of range. Must be non-negative and less than the size of the collection. Parameter name:
index'
I am fetching data from db and passing to view with different set of data.
List<MasterEntity> ListOfmasterEntity = new List<MasterEntity>();
ListOfmasterEntity.Add(masterEntityA);
ListOfmasterEntity.Add(masterEntityB);
return View(ListOfmasterEntity)
I have instantiated my master like below. MasterEntity is super class that contains List where T is various entities
public class PageEntity
{
public PageEntity()
{
}
public string DesignId { get; set; }
public string DesignName { get; set; }
public string DesignStatus { get; set; }
}
Master Class
public MasterEntity()
{
this.ListOfPageEntity = new List<PageEntity>();
this.ListOfuserEntity = new List<UserEntity>();
}
public List<UserEntity> ListOfuserEntity { get; set; }
public List<PageEntity> ListOfPageEntity { get; set; }
On the view page when I do LINQ my code breaks as followes.
#foreach (var item in Model.First().ListOfPageEntity)
{
//This brings data for n times then 1 more lookup in collection is breaking the code. I don't exactly know why!
}
OK. So finally I got the answer after spending quite some hours in debugging. Like it happen in coding time it turn out a silly.
Short answer : I din't handled null on cshtml where I cast it into array.
Description :
From my controller I am passing MasterObject to view. MasterObject is blue print of various other collections objects. There are some dynamic values are populating in MasterObject. While rendering the razor view I called the property to render it but actully it was never initialzed since there was no table returned for it. So, I needed to handle null explicitly. Finally, got it done.
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.
I'm trying to do what I thought would be a very simple think using Linq lambda, it probably is, but I can't find an example in any tutorial.
I have a simple class with a few properties. I want to get a list of one of the properties based on the value on another value in that class.
Below is an example of the code, using Linq to get the correct results:
public class Client
{
public int ClientId { get; set; }
public int ClientWorth { get; set; }
public strin ClientName { get; set; }
}
.
.
.
.
List<Client> allClients = this.GetAllClients();
List<string> richClients = (
from c in allClients
where c.ClientWorth > 500
select c.ClientId.ToString()).ToList();
Can someone tell me how to do this using a lambda
I can do the following:
List<Clients> richClients = allClients.Where(x => x.ClientWorth >500)
Which give me a list of all clients, but I would like to get a string list back with just the client ids.
After filtering by client worth value you should project results - i.e. select only client id value:
allClients.Where(c => c.ClientWorth > 500).Select(c => c.ClientId.ToString()).ToList()
Further reading: Enumerable.Select
SOLVED:
The URI was incorrect. Was "h||p://#.#.#.#/:9200" and should have been "h||p://#.#.#.#:9200". This was causing the API to change the port number to 80. Surprised the API actually was able to connect to ElasticSearch instance with the incorrect port number.
I'm new to NEST and ElasticSearch and trying to put together a a simple MatchAll query in NEST.
When I perform a MatchAll from Sense
POST /movies/movie/_search
{
"query": {
"match_all": {}
}
}
I get all the movie objects in the movies index.
But when I try the NEST query
var result = client.Search(s => s.Type("movie").MatchAll());
I get nothing back. Tried setting the return type to a movie class, and still no results.
public class Movie
{
public string title { get; set; }
public string director { get; set; }
public int year { get; set; }
public List<string> genres { get; set; }
}
Also tried .AllIndices() and/or .AllTypes() per this reply
Searching an elasticsearch index with NEST yields no results
Any ideas?
EDIT:
Heres the connection string setting the default index.
ConnectionSettings connection = new ConnectionSettings(uri).UsePrettyResponses().SetDefaultIndex("movies");
You have to check for IsValid on result to see if the call succeeded or not.
result.ConnectionStatus will hold all the information you need to determine what went wrong.
If you'd like to throw exceptions instead you can enable that by calling:
.SetConnectionStatusHandler(c=> {
if (!c.Success)
throw new Exception(c.ToString());
})
on your ConnectionSettings
Calling ToString on an ConnectionStatus object prints all the request and response details in human readable form.