Entity Framework 6 - Knowledge Base (KB)
63 results in tag: lambda
Building where clauses to evaluate collections inside a many to many connection using LINQ to entities
So, I am using the Linq entity framework. I have 2 entities: ...Content... and ...Tag.... They are in a many-to-many relationship with one another. ...Content... can have many ...Tags... and ...Tag... can have many ...Contents.... So I am trying to write ...
asked by Phobis
Where Predicate Type Arguments in C#
I have an XElement with values for mock data. ...I have an expression to query the xml:...Expression<Func<XElement, bool>> simpleXmlFunction = b => int.Parse(b.Element("FooId").Value) == 12; ...used in:...var simpleXml = xml.Elements("Foo").Where(si...
asked by blu
Parent Navigation Property C# Expression Tree Parameter
How can I create a ParameterExpression for the parent side of a 1 to * Navigation Property?...The following works for the child entity:...var parameter = Expression.Parameter( typeof(T), // where T is the entity type GetParameterName()); // helper...
asked by blu
How may two C# Lambda Expressions be combined without using an invoke?
I'd like to merge the following Expressions:...// example class class Order { List<OrderLine> Lines } class OrderLine { } Expression<Func<Order, List<OrderLine>>> selectOrderLines = o => o.Lines; Expression<Func<List<OrderLine>, Boolean>> vali...
asked by Davy Landman
Because string is not a delegate type, Entity Framework cannot convert lambda expressions to it.
I am using Entity Framework in my C# based code. I am running into an unexpected weirdness and am looking for suggestions....Case 1, 2, 3, 4... Projects:... RivWorks.dll... RivWorks.Service.dll... RivWorks.Alpha.dll ...Samples (all of these work):...Riv...
asked by Keith Barrows
In Expression Trees, working with nullable types
I have an extension method to dynamically filter Linq to Entities results using string values. It works fine until I use it to filter nullable columns. Here's my code:...public static IOrderedQueryable<T> OrderingHelperWhere<T>(this IQueryable<T> source, ...
asked by dstr
Expression Tree's like operator
I have a Linq extension method to dynamically filter Linq queries using string values. For example: ...query.WhereHelper("columName", ">", 1).... I could use many different filter operators like GreaterThan or NotEqual etc. but not "Like". There is no Exp...
asked by dstr
Entityframework Join using lambdas and the join method
It seems there are different ways to do joins using linq. One is more straightforward and involves just joining tables like this:...var found = from c in s.categories join cm in s.categorymaps on c.CategoryId equals cm.ChildCategoryId ...
asked by Mason
Using C#, convert a lambda expression to a SQL UPDATE query.
Is library or code available to create SQL Update statements from lambda expressions? We would like to use strongly-typed lambda expressions to do updates instead of calling the object before hand, or using strings. I'm thinking of something like this..
asked by Sterling Nichols
LINQ and Entity Framework are used to check for null values in C# variables.
I'm quite new to LINQ & Entity framework as well as the var keyword in c# so please pardon me if this sounds like a 'newbie' question. ...I have problems checking for null values after doing something like this: ...var entry = myDB.Entries.Where(e => e.Em...
asked by yulun
Should I use lambda or LINQ for a multi-table join in Entity Framework 4.1?
I'm new to the Entity Framework and I'm trying to convert a multi table join to use the Entity framework. The original SQL looked something like this...JOIN tab_NewsCommunities S1 ON S1.News_ID = tab_News.NewsID inner join tab_communities com on S1.Commu...
asked by NullReference
lambda expression for left join
I have tableA and tableB.... I would like to perform left join using lambda expression. This is the equal sql statement:...SELECT * FROM tableA A LEFT JOIN tableB B ON A.userId=B.userId ...How can I do that using lambda expression?
asked by Naor
IN clause mistake in C# lambda
I’m having issues creating an IN clause using C# and lambdas....I have the following method ...GetUserList(string filtersByRoles)...The variable ...string filtersByRoles... can hold a comma-delimited value such as: “1,2†or “1,2,3†or “1,3,4â€...
asked by Vlince
Using lambda to group by several columns
How can I group by with multiple columns using lambda?...I saw examples of how to do it using linq to entities, but I am looking for lambda form.
asked by Naor
If the query is empty, the maximum return value
I have this query:...int maxShoeSize = Workers .Where(x => x.CompanyId == 8) .Max(x => x.ShoeSize); ...What will be in ...maxShoeSize... if company 8 has no workers at all?...UPDATE:... How can I change the query in order to get 0 and not an excep...
asked by Naor
How can I make a partial SQL query from an expression tree?
When EF or LINQ to SQL runs a query, it:...Builds an expression tree from the code,...Converts the expression tree into an SQL query,...Executes the query, gets the raw results from the database and converts them to the result to be used by the applicatio...
asked by Arseni Mourzenko
Where Clause with Enums in Entity Framework
So here is what I have for my enum. Really basic. The enum does NOT have a corresponding database table. Rather, whenever a class has a MyEnum property, the database has an int column. That all works fine....public enum MyEnum : int { Zero = 0, On...
asked by Alec
Where Clause in the Entity Framework
Let's say i have a table named User. When I use the Entity Framework to get the records i do like this:...var db = new Context(); var users = db.Users; ...It return all the users in my table. OK. If i do this:...var fooUsers = db.Users.Where(u => u.Name =...
asked by Rodrigo Manguinho
A where clause in a linq to entities clause? (inner location)
I have a table with a one to many mapping to a table that has a many to many mapping to another table. I'd like to do the following:...var results = context.main_link_table .Where(l => l.some_table.RandomProperty == "myValue" && ...
asked by L2Eer
How to query a list inside a list using Linq?
I have Store List (storeList) object. (Consists of list of Stores) Each Store has list of Addresses. Each address have AddressType property that can be PHYSICAL, ALTERNATIVE or MAILING....I am trying to return PHYSICAL Address object so I can modify its p...
asked by bobetko
