Expression Tree Tutorial - Knowledge Base (KB)
66 results in tag: entity-framework
How do I build a Linq Expression Tree that compares against a generic object?
I have an IQueryable and an object of type T....I want to do IQueryable().Where(o => o.GetProperty(fieldName) == objectOfTypeT.GetProperty(fieldName))...so ......public IQueryable<T> DoWork<T>(string fieldName) where T : EntityObject { ... T...
asked by JTew
How do I apply OrderBy on an IQueryable using a string column name within a generic extension method?
public static IQueryable<TResult> ApplySortFilter<T, TResult>(this IQueryable<T> query, string columnName) where T : EntityObject { var param = Expression.Parameter(typeof(T), "o"); var body = Expression.PropertyOrField(param,columnName); var sor...
asked by JTew
C# LINQ Where Predicate Type Arguments
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
C# Expression Tree Parameter for Parent Navigation Property
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 to create LINQ Expression Tree to select an anonymous type
I would like to generate the following select statement dynamically using expression trees:...var v = from c in Countries where c.City == "London" select new {c.Name, c.Population}; ...I have worked out how to generate...var v = from c in ...
asked by Tom Deloford
How to wrap Entity Framework to intercept the LINQ expression just before execution?
I want to rewrite certain parts of the LINQ expression just before execution. And I'm having problems injecting my rewriter in the correct place (at all actually)....Looking at the Entity Framework source (in reflector) it in the end comes down to the ...
asked by Davy Landman
LinqKit System.InvalidCastException When Invoking method-provided expression on member property
Given a simple parent/child class structure. I want to use linqkit to apply a child lambda expression on the parent. I also want the Lambda expression to be provided by a utility method....public class Foo { public Bar Bar { get; set; } } public cl...
asked by user293499
Working with nullable types in Expression Trees
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
Like operator in Expression Tree
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
Entity Framework - Linq - Unable to create a constant value of type ‘System.Object’. Only primitive types
I have a method to build an expression for a linq query for a given type, property, and value. This works wonderfully as long as the property on the type is NOT nullable. Here is the example I am working from (...http://www.marcuswhitworth.com/2009/12/dyn...
asked by Shane
Calling the .Any Extension Method with Entity Framework using Expression Trees
I have looked at few examples here ...Calling a Method from an Expression... and on ...MSDN... but I have not been able to get the right method call/object type for Any() for the query below. I seem to be able to get the property call but not IEnumerable ...
asked by RCrabtree
How to reflect over T to build an expression tree for a query?
I'm trying to build a generic class to work with entities from EF. This class talks to repositories, but it's this class that creates the expressions sent to the repositories. Anyway, I'm just trying to implement one virtual method that will act as a base...
asked by Gup3rSuR4c
Expression Trees and Nullable Types
I've been playing around with Expression Trees. I have the following simple method that performs a query by dynamically creating an Expression Tree. ItemType is a nullable int in the database, ...and also in the EF entity class.... For some reason thou...
asked by Adam Rackis
Why is a conversion necessary in Expression Trees
From ...this question... I asked 5 minutes ago, it's clear that the following code throws an exception, stating that ...Unhandled Exception: System.InvalidOperationException: The binary operator Equal is not defined for the types 'System.Nullable`...
asked by Adam Rackis
How do I rewrite query expressions to replace enumerations with ints?
Inspired by a desire to be able to use enumerations in EF queries, I'm considering adding an ExpressionVisitor to my repositories that will take incoming criteria/specifications criteria and rewrite them to use the corresponding persisted int property....
asked by Morten Mertner
How to assign a property value of an IQueryable<T>?
I'm using Entity Framework 4.1 Code First. In my entity, I have three date/time properties:...public class MyEntity { [Key] public Id { get; set; } public DateTime FromDate { get; set; } public DateTime ToDate { get; set; } [NotMap...
asked by Matt Johnson-Pint
Need to build expression tree for max date value
I'm trying to build an expression tree for this linq query: so I can pass in a generic Entity:...this.EntityCollection.Select((ent) => ent.TimeStamp).Max() ...I am wanting to create a class that takes a generic Entity and finds the max of its TimeStamp pr...
asked by Adam
How compose Expression: selector + predicate?
Assume that we have two classes...public class EntityA { public EntityB EntityB { get; set; } } public class EntityB { public string Name { get; set; } public bool IsDeleted { get; set; } } ...And two expressions for selector and predicator..
asked by qmicron
Entity Framework Hitting 2100 Parameter Limit
I'm migrating some of our code from LINQ-to-SQL to Entity Framework. Previously, when run up against a 2100 parameter limit from SQL Server (described ...here...), I used the solution provided by Marc Gravell ...here.... As stated in his own response, it ...
asked by Ocelot20
How to create dynamic condition using Expression Tree
Please consider this code:...System.Linq.Expressions.Expression<Func<tbl, bool>> exp_details = r => r.ID_Master == Id && r.Year == Year && r.Month == Month ; ...I want to write a function that expect some argument, and then retrieve some data from my data...
asked by Arian
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