I have class which has ICollection of Images. I need to bring only single image from database:
var object=db.Context.Where(l=>l.Name=="John" &&
l.Images==l.Images.Single())
The query above is not correct. Can someone help how to return only single image from ICollection of Images?
Thanks
I'm not sure of the structure of your classes, but possibly something like this:
var object = db.Context.FirstOrDefault(l => l.Name == "John");
or
var object = db.Context.FirstOrDefault(l => l.Name == "John").Images.FirstOrDefault();
I think this is what you need:
var object=db.Context.Where(l=>l.Name=="John").FirstOrDefault();
FirstOrDefault expects zero or more results and you only want the first item on the result.
You could try the next code:
var singleImage=db.Context.Where(n=>n.Name=="John").Select(m=>m.Images).FirstOrDefault();
Related
I'm using the Mongo LINQ Driver for C#, works great.
Sorting a lot of properties but heres a problem I can't solve, its probably simple.
var identifierList = new []{"10", "20", "30"};
var newList = list.Where(x => identifierList.Contains(x.Identifier));
This is NOT supported ...
So I could do something like:
var newList = list.Where(x => x.Identifier == "10" || x.Identifier == "20" || x.Identifier == "30");
But since the list is variable ... how do I construct the above? Or are there even better alternatives?
The list is of type IQueryable<MyCustomClass>
For information ... this is used as a filter of alot of properties. In SQL I could have a parent -> child relationship. But as I can't as the parent for the main ID I need to take all the ID's out and then construct it like this.
Hopes this makes sense. If needed I will explain more.
To answer my own question ... The Mongo Sharp LINQ driver has an extension method called "In" which does exactly what I need.
They have however implemented it in 1.5 so we can use the old way like: https://jira.mongodb.org/browse/CSHARP-462
var list = new []{"10", "10"};
search.Where(x => list.Contains(x.Id));
But the version 1.5 package is not on nuget yet.
However, this should work with the "In" extension that comes as a special surprise with the mongo-csharp-driver.
search.Where(x => x.In(list));
var identifierList = new []{"10", "20", "30"};
var newList = list.ToList().Where(x => identifierList.Contains(x.Identifier));
You will just have to use List instead of Ienumerable (do that by using the .ToList())
If it doesn't work please add your list TYPE
I have an IEnumerable variable that I want to extract a distinct value from. I know all the entries in the rows of the list have the same value, I just need to get that value.
The method returns an IEnumerable.
The row in the IEnumerable is defined as:
QuoteCovId
AdditionalInterestId
AdditionalInterestsAffiliateId
AdditionalInterestsLastName
AdditionalInterestsBusinessAddrLine1
AdditionalInterestsBusinessCity
AdditionalInterestsBusinessState
AdditionalInterestsBusinessZip
Sampel of code:
IadditionalInterestData = AdditionalInterestData.GetAdditionalInterests(MasterPkgID, Requestor);
// Using linq.
var quotes = from ai in IadditionalInterestData
select Distinct(ai.QuoteCovId);
// Iterate thru to get the 1 value.
foreach (int QuoteCovId in quotes)
{
quoteID = QuoteCovId;
}
var quoteId = AdditionalInterestData.GetAdditionalInterests(MasterPkgID, Requestor)
.FirstOrDefault().Select(f => f.QuoteCovId);
But that method:
AdditionalInterestData.GetAdditionalInterests(MasterPkgID, Requestor);
returns me an IEnumerable which I will use further in my application. Which is what I need.
So how will your suggestion still give me that IEnumerable and give me the quote value which happens to be the same in the collection?
var quoteId = AdditionalInterestData.GetAdditionalInterests(MasterPkgID, Requestor).FirstOrDefault().Select(f => f.QuoteCovId);
Also, I just added your line of code as is and I get an error statement.
I am trying to perform an update using strongly-typed objects. For example,
public void setAppointmentPrefs(string UserName, IEnumerable<AppointmentInfo> info)
{
var query = new QueryDocument {{ "ProviderId", UserName}};
var update = Update.Set("Prefs",prefs); // prefs.toList() gives same error
// providerprefs initialized in constructor
providerprefs.Update(query, update);
}
I receive a compiler error saying:Error 14 The best overloaded method match for 'MongoDB.Driver.Builders.Update.Set(string, MongoDB.Bson.BsonValue)' has some invalid arguments
Obviously the Mongo driver will not let me update based on my own object (whether as IEnumerable or prefs.toList()), which seems a contrast from the way it permits me to insert or query with custom objects. Surely I am missing something obvious that would permit me to avoid deserializing, weakly typing then creating a generic BsonDocument!! TIA.
You can do an Update based on your own types! Have you tried using the typed Query and Update builders?
Try something like this:
var query = Query<AppointmentInfo>.EQ(i => i.ProviderId, userName);
var update = Update<AppointmentInfo>.Set(i => i.Prefs, info.Prefs);
Not sure I got the types and everything write from your partial code, but that should give you the general idea.
Let me know if you have any further questions.
I know this has been answered but I for one don't fully understand Roberts answer.
All I did is call the "ToBsonDocument()" method for it to except the object as a parameter
So:
customObject.ToBsonDocument()
If you have an array of objects inside a document:
var query = Query.EQ("_id", ObjectId.Parse(id.ToString()));
var update = Update.Push("ArrayOfObjects", customObject.ToBsonDocument());
collection.Update(query, update);
I have a situation where I'm trying to filter a LINQ select using a derived sub class.
ctx.BaseEntity.OfType<SubClass>() - this works fine.
However I'd like to do this using a string value instead. I've come across a performance barrier when I have lots (>20) Sub Classes and selecting an Entity without using OfType just isn't an option. I have a generic UI that renders from the base class, so I don't know what Class Type will be returned at compile time.
So what I'd like to do is this:
Perform a projected Select where I
return just the SubClassType from
the database
Perform a second select
using this value as the OfType to
only select the relevant related
entity from the database (No mass
unions generated)
int id = 1;
var classType = (from c in ctx.BaseClass.Include("ClassType")
where c.id == id
select new
{
c.ClassType.TypeName
}).First();
BaseClass caseQuery = ctx.BaseClass.OfType<classType.TypeName>()
.Include("ClassType")
.Include("ChildEntity1")
.Include("ChildEntity2")
.Where(x => x.id== id);
But obviously this won't work because OfType requires a Type and not a string.
Any ideas on how I can achieve this?
Update:
As a side note to the original question, it turns out that the moment you project a query that uses a Navigation Property - it builds the monster SQL too, so I've ended up using a stored procedure to populate my ClassType entity from the BaseClass Id.
So I've just got it to work using eSQL, which I'd never used before. I've posted the code here just in case it helps someone. Has anyone else got a more strongly typed solution they can think of?
BaseClass caseQuery = ctx.BaseClass.CreateQuery<BaseClass>("SELECT VALUE c FROM OFTYPE(Entities.[BaseClass],namespace.[" + classType.TypeName + "]) as c")
.Include("ClassType")
.Include("ChildEntity1")
.Include("ChildEntity2")
.Where(x => x.id== id).FirstOrDefault();
To answer the headline question about calling OfType with a string / runtime type, you can do the following:
// Get the type, assuming the derived type is defined in the same assembly
// as the base class and you have the type name as a string
var typeToFilter = typeof(BaseClass)
.Assembly
.GetType("Namespace." + derivedTypeName);
// The use reflection to get the OfType method and call it directly
MethodInfo ofType = typeof(Queryable).GetMethod("OfType");
MethodInfo ofTypeGeneric = method.MakeGenericMethod(new Type[] { typeToFilter });
var result = (IQueryable<Equipment>)generic.Invoke(null, new object[] { equipment });
Combine this with your stored procedure to get the class name and you (should?) avoid the massive join - I don't have table-per-type implementation to play with so I can't test.
I have two tables in my entity framework, objects, and parameters which have a foreign key pointing to the object to which they belong. I want to populate a tree with all the attributes of a certain object. So in order to find those I want to do this:
String parentObject = "ParentObjectName";
var getAttributes = (from o in myDB.ATTRIBUTE
where o.PARENT_OBJECT == parentObject
select o);
However when I try to do this I get an error saying it cannot convert from type OBJECT to string, even though in the database this value is stored as a string. I have a workaround where I get an instance of the parentObject, then go through every attribute and check whether it's parent_object == parentObjectInstance, but this is much less efficient than just doing 1 query. Any help would be greatly appreciate, thanks!
Well, PARENT_OBJECT.ToString() can't be called (implicitly or explicitly) in L2E, but if it just returns a property, you can look at that directly:
String parentObject = "ParentObjectName";
var getAttributes = (from o in myDB.ATTRIBUTE
where o.PARENT_OBJECT.NAME == parentObject
select o);
...note the .NAME
Try this:
String parentObject = "ParentObjectName";
var getAttributes = (from o in myDB.ATTRIBUTE
where o.PARENT_OBJECT.ToString() == parentObject
select o);