I Need some help with C# Mongo Driver and mongodb.
C# class example:
public class Document
{
public string Id { get; set; }
public DateTime StartTime { get; set; }
public TimeSpan CustomPeriod { get; set; }
}
I need a way to find documents in mongodb by StartTime field + some TimeSpan value, like this predicate:
Expression<Func<Document, bool>> customExpression = x
=> x.StartTime.Add(x.CustomPeriod) <= DateTime.UtcNow;
These predicates are not working and I am getting an error when executing Collection.Find() query now:
{document}{StartTime}.Add({document}{CustomPeriod}) is not supported.
The issue is the query language used by the underlying find command at the MongoDB instance does not support comparing one field in a document with another, or performing operations on these fields before comparison.
The $expr operator permits using aggregation expressions, but you usually forfeit the ability to use an index for that portion of the query.
In the mongo shell that might look like:
db.collection.find({
$expr:{
$gte:[
new Date(),
{$add: [ "$StartTime", "$CustomPeriod"]}
]
}
})
I'm not familiar with C#, so I don't know how to express that using the .net driver
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 work with a old database where everything is saved as a string. I have a client table and this table has a status column. I also use entity framework code first. Still version 6. I used reverse engineering system to start a code first from database at beginning.
[StringLength(1)]
public string status { get; set; }
What you need to understand is that everything that should be an enum in a good database design is a string in my database. In my C# I would like to use the enum. How can I do to save a enum as a string by default in my database and read is has a string and parse it as a enum?
Given
public enum MyFunkyEnum
{
SomeValue
}
You could just use a calculated property that is not in the actual db schema
public string status { get; set; }
public MyFunkyEnum MyFunkyEnumStatus => (MyFunkyEnum)Enum.Parse(typeof(MyFunkyEnum), status);
Note : You will need to use tweak the logic if you have null or empty strings
or both directions
[NotMapped]
public MyFunkyEnum MyFunkyEnumStatus
{
get => (MyFunkyEnum) Enum.Parse(typeof(MyFunkyEnum), status);
set => status = value.ToString();
}
I'd like to retrieve data from mongodb using a c# driver and I'm having difficulty to use aggregation framework to retrieve documents async.
I have more than hundread thousand documents and trying to get all id's async is taking too long to get back all id's.
Base on all id's i am iterate foreach loop enter code here match that id and -get that documents data but while retrieve data I like to use $substr
-on list of string see the attached raw data set.
+e.g in db = string["one", "two", "three"]
in query looking while iterate list of string["ne","wo","hr"]
C# Model:
public class ThirtyTwoZero
{
public ObjectId Id { get; set; }
public string SequenceNo { get; set; }
public List<string> ThirtyTwoZeroList { get; set; }
}
First DocumentSet
Secound DocumentSet
Appreciate for any help and Thanks in advance!
My goal is to put a "deleted at" timestamp on specific object in an array of a document.
If the document looks like this:
{
"subdoc": [
{
"key": 1,
"value": "abc",
"isActive": true
},
{
"key":5,
"value": "ade",
"isActive":true
}
]
}
I would like to be able to say "look for the document that has subdoc.key == 5 and subdoc.value == "ade"; set subdoc.isActive to false and set subdoc.deleteAt = current db timestamp. With a resulting document like this:
{
"subdoc": [
{
"key": 1,
"value": "abc",
"isActive": true
},
{
"key":5,
"value": "ade",
"isActive": false,
"deletedAt": Timestamp(1425911075,1)
}
]
}
Is this doable?
Update: After further review of the mongo docs, this does seem doable with the "$ (update)" operator. That gets me what I need, but I'm hoping for a less magical-strings way of doing this using the C# driver?
My working find/update looks like this:
// find
{
"subdoc.key":"2",
"subdoc.value":"ade"
}
// update
{
"$currentDate": {
"subdoc.$.deleteAt": {
"$type": "timestamp"
}
}
}
Update: I should clarify that this updated time stamp field is used for synchronization by many sometimes-connected mobile clients in a load-balanced environment (multiple web servers, multiple worker processes, and a mongo cluster) with a high transaction volume, which makes it crucial that this time stamp has a single point truth, is logically sequential in the context of the app, and is as high precision as possible (fractions of a second). Otherwise, records could be missed in a sync.
For the moment, I'm using the above approach to ensure time stamped values are generated by the mongo database instance. And I'm pretty satisfied with this approach.
you can use the c# driver to wrap the mongo entities in c# objects. Then in your code you can use linq to query the DB and update your objects as required. Then just save them to the DB to persist your changes.
Below is a small piece of code to query a Parent collection in the test DB.
The C# driver provides as AsQueryable extension to allow us to write our queries directly in Linq. The driver will then automatically build the required query and execute it against the collection.
The sample below looks for any sub documents in the subdoc list that have a value on the key field of 5
If it finds any, it updates the deletedAt date and then saves it back to the DB.
var client = new MongoClient();
var database = client.GetServer().GetDatabase("test");
var parentCollection = database.GetCollection<Parent>("Parent");
var parent = parentCollection.AsQueryable().FirstOrDefault(p => p.subdoc.Any(f => f.key == 5));
if (parent != null)
{
var fooList = parent.subdoc.Where(f => f.key == 5);
foreach (var foo in fooList)
{
foo.deletedAt = DateTime.UtcNow;
}
}
parentCollection.Save(parent);
Below are the two c# entities used to map to the Mongo documents. We can use the [BsonIgnoreIfNull] attribute of the mongo c# driver to only serialize the deletedAt field if it contains a value. We also use a nullable DateTime object in our code to allow nulls to be stores if required.
public class Foo
{
[BsonId]
public ObjectId Id { get; set; }
public int key { get; set; }
public string value { get; set; }
public bool isActive { get; set; }
[BsonIgnoreIfNull]
public DateTime? deletedAt { get; set; }
}
public class Parent
{
[BsonId]
public ObjectId Id { get; set; }
public List<Foo> subdoc { get; set; }
}
See most recent update. A combination of the positional and $currentDate operators is serving my purpose.
I use Neo4jClient to use Neo4j, I use cypher code for CRUD entity , Follow code :
_graphClient.Cypher.Merge("(n:Movie { Id:101 })")
.Set("n.Key = 55,n.DateTime='" +DateTime.UtcNow.ToString()+"'").ExecuteWithoutResults();
_graphClient.Cypher
.Match("(n:Movie)-[r:RelName]-(m:Movie)")
.Where((EntityNode n) => n.Id == 20)
.Return.......
public class EntityNode
{
public int Id { get; set; }
public string Key { get; set; }
public DateTime DateTime { get; set; }
}
ERROR :Neo4j returned a valid response, however Neo4jClient was unable to deserialize into the object structure you supplied.Can't deserialize DateTime.
On other hand i use jsonconvertor in different ways, for example :
_graphClient.Cypher.Merge("(n:Movie { Id:101 })")
.Set("n.Key = 55,n.DateTime=" +JsonConvert.SerializeObject(DateTime.UtcNow)).ExecuteWithoutResults();
I still have the ERROR
Pass it as a proper parameter:
graphClient.Cypher
.Merge("(n:Movie { Id:101 })")
.Set("n.Key = {key}, n.DateTime = {time}")
.WithParams(new {
key = 55,
time = DateTimeOffset.UtcNow
})
.ExecuteWithoutResults();
This way, Neo4jClient will do the serialization for you, and you don't introduce lots of security and performance issues.
This is in the doco here: https://github.com/Readify/Neo4jClient/wiki/cypher#parameters
I have faced the same issue recently its because of date time value coming from neo.
I have stored the date time in neo as epoch time but while retrieving i used long in the class. because of this its given me the above error.
Try using string for the above date time.
Hope this helps you.