I am trying to use Joseph Albahari's PredicateBuilder with my applications Respository which is giving me the following error:
The best overloaded method match for 'MySite.DAL.Respositories.IMyObjRepository.SearchFor(System.Linq.Expressions.Expression<System.Func<MySite.DAL.MyObj,bool>>)' has some invalid arguments
Signiture for MySite.DAL.Respositories.IMyObjRepository.SearchFor:
public IQueryable<MyObj> SearchFor(Expression<Func<MyObj, Boolean>> predicate)
Code calling SearchFor:
var predicate = PredicateBuilder.True<MySite.DAL.MyObj>();
predicate = predicate.And(a => a.county.name == CountyName);
return _myObjRespository.SearchFor(predicate);
I am aware that I do not need PredicateBuilder for this query - I have simplified it for the purposes of this question. The simplified version still gives the same error.
Any help/ideas/advice appreciated.
Thank you.
I have just discovered the type expected in _myObjRespository.SearchFor() did not match the type I was setting/sending in var predicate = PredicateBuilder.True();
MyObj was replacing my object names for security/confidentiality reasons - I accidently replaced the different types on my original post.
Related
I have simplified the following example from my code and hoping there's no obvious compilation errors because of it. Lets say I have the following entities (not what i actually have, please assume I have no EF or schema issues, this is just for example):
public class Company
{
public string GroupProperty {get;set;}
public virtual ICollection<PricingForm> PricingForms {get;set;}
}
public class PricingForm
{
public decimal Cost {get;set;}
}
And I want to query like so:
IQueryable DynamicGrouping<T>(IQueryable<T> query)
{
Expression<Func<Company, decimal?>> exp = c => c.PricingForms.Sum(fr => fr.Cost);
string selector = "new (it.Key as Key, #0(it) as Value)";
IQueryable grouping = query.GroupBy("it.GroupProperty", "it").Select(selector, exp);
return grouping;
}
I get the following error when calling the groupby/select line:
System.Linq.Dynamic.ParseException: 'Argument list incompatible with lambda expression'
What type is "it" when grouped? I have tried using other expressions that assume it is an IGrouping<string, Company>, or a IQueryable<Company>, same error. I've tried just selecting "Cost" and moving the Sum() aggregate into the selector string (i.e. Sum(#0(it)) as Value) and always seem to get the same error.
I eventually tried something along the lines of:
Expression<Func<IEnumerable<Company>, decimal?>> exp = l => l.SelectMany(c => c.PricingForms).Sum(fr => fr.Cost);
However this one, I get farther but when attempting to iterate through the results I got a different error.
The LINQ expression node type 'Invoke' is not supported in LINQ to Entities.
So, with this dynamic grouping and injecting my own select expression, what should I assume the datatype of 'it' is? Will this even work?
The type of it is IGrouping<TKey, TElement>, where TKey is dynamic based on the keySelector result type, and TElement is the element type of the input IQueryable. Luckily IGrouping<TKey, TElement> inherits (is a) IEnumerable<TElement>, so as soon as you know the input element type, you can safely base selector on IEnumerable<TElement>.
In other words, the last attempt based on Expression<Func<IEnumerable<Company>, decimal?>> is correct.
The new error you are getting is because #0(it) generates Expression.Invoke call which is not supported by EF. The easiest way to fix that is to use LINQKit Expand method:
Expression<Func<Company, decimal?>> exp = c => c.PricingForms.Sum(fr => fr.Cost);
string selector = "new (it.Key as Key, #0(it) as Value)";
IQueryable grouping = query.GroupBy("it.GroupProperty", "it").Select(selector, exp);
// This would fix the EF invocation expression error
grouping = grouping.Provider.CreateQuery(grouping.Expression.Expand());
return grouping;
I have this working Code
var h = db.MyTable.Include("Children").Include("Parent").ToList();
but when I add where condition
var h = db.MyTable.Include("Children").Include("Parent").Where(x => x.Country==Session["country"].ToString()).ToList();
it throws me an error
LINQ to Entities does not recognize the method 'System.Object get_item (System.String)' method , and this method cannot be translated into a store expression.
How can i rewrite it ? Im beginner :-)
Thank you
This is caused by your Where-Expression. You should only use variables in there or call methods that can be translated to SQL.
First, save your Session value in a variable:
var country = Session["country"].ToString();
Then use country in your Where-Expression.
MSDN provides a list of methods you can use inside LINQ to SQL expressions and how they are mapped to SQL functions.
try this:
var t = Session["country"].ToString();
var h = db.MyTable.Include("Children").Include("Parent").Where(x => x.Country==t).ToList();
only activities can be parsed into expression-tree that is supported by your provider
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);
In general, If I create an extension method that acts on an entity:
public static MyEntity Foo(this MyEntity entity)
{
// do something to the entity
}
One cannot directly use this in a projection from Linq-To-Entities such as follows:
var result = myContext.MyEntities.Select(x=> x.Foo());
Doing so yields an error such as:
System.NotSupportedException: LINQ to Entities does not recognize the
method 'Foo(MyEntity)' method, and this method cannot be translated
into a store expression.
I fully understand why this error occurs. My question is this: If I can provide an implementation of Foo that uses an expression tree, is there some way that I can add Foo to the operations that LINQ-to-entities understands? And if so - how?
Note: I can certainly convert it to a list like this:
var result = myContext.MyEntities.ToList().Select(x=> x.Foo());
And it doesn't error. But I no longer have an IQueryable. I have an IEnumerable. If I were to use it like this:
var result = myContext.MyEntities.ToList().Select(x=> x.Foo()).First();
I would end up fetching ALL entities before taking the top one and discarding the rest - which would be horrible for performance.
Use LINQKit project, but instead of your method foo, You will be obliged to write expression tree which is equivalent.
I'm using MVC and Entity Framework. I've created a class in my model folder with this code below. I keep getting the error message above with both queries below. I know there is a known issue on referencing non-scalar variables, but I'm not sure how to implement a workaround:
http://msdn.microsoft.com/en-us/library/bb896317.aspx#Y1442
private MovieLibraryDBEntities movieLibraryDBEntitiesContext;
public int getNumberOfEntriesReserved()
{
return (from m in movieLibraryDBEntitiesContext.Movies
where m.CheckedOut.Equals(1)
select m).Count();
//return movieLibraryDBEntitiesContext.Movies
// .Where(e => e.CheckedOut.Equals(1))
// .Select (e => e.Title).Count();
}
You cannot use m.CheckedOut.Equals(1) in linq-to-entities query. Use m.CheckedOut == 1 but CheckedOut must be integer.
This is an older question. I had the same problem when trying to filter a nullable column using the IQueryable interface. I solved the problem by first checking to see if the object had a value and then checking the value.
widgets = widgets.Where(x => x.ID.HasValue.Equals(true) && x.ID.Value.Equals(widgetID));
same issue using Any()
i had to change my where clause to search on primitive types, for me int
so this
where order.User == user
becomes this
where order.User.UserId == user.UserId
There is a blog post explaining the quirk.