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combing two linq expressions


combing two linq expressions

By : Toni Henriksson
Date : November 22 2020, 12:01 PM
I wish this help you You already can use your expressions in repository without outer combining them:
code :
var yourContext = getContext();
var filtered = yourContext.Where(filter).Where(filter2);
public class ReplacementVisitor : System.Linq.Expressions.ExpressionVisitor
{
    private readonly Expression _oldExpr;
    private readonly Expression _newExpr;
    public ReplacementVisitor(Expression oldExpr, Expression newExpr)
    {
        _oldExpr = oldExpr;
        _newExpr = newExpr;
    }

    public override Expression Visit(Expression node)
    {
        if (node == _oldExpr)
            return _newExpr;
        return base.Visit(node);
    }
}
Expression<Func<Customer, bool>> filter = c => c.Active;
Expression<Func<Customer, bool>> filterz = c => c.Visible;

var newParameter = Expression.Parameter(typeof(Customer), "x");
var visitor1 = new ReplacementVisitor(filter.Parameters[0], newParameter);
var visitor2 = new ReplacementVisitor(filterz.Parameters[0], newParameter);

var newLambda = Expression.Lambda(
    Expression.AndAlso(
        visitor1.Visit(filter.Body),
        visitor2.Visit(filterz.Body)
    ),
    newParameter
);


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Unable to cast object of type 'System.Linq.Expressions.UnaryExpression' to type 'System.Linq.Expressions.MemberExpressio

Unable to cast object of type 'System.Linq.Expressions.UnaryExpression' to type 'System.Linq.Expressions.MemberExpressio


By : Knante
Date : March 29 2020, 07:55 AM
it helps some times You need a separate line to extract the Member where the input expression is a Unary Expression.
Just converted this from VB.Net, so might be slightly off - let me know if I need to make any minor tweaks:
code :
public string GetCorrectPropertyName<T>(Expression<Func<T, Object>> expression)
{
    if (expression.Body is MemberExpression) {
        return ((MemberExpression)expression.Body).Member.Name;
    }
    else {
        var op = ((UnaryExpression)expression.Body).Operand;
        return ((MemberExpression)op).Member.Name;
    }                
}
Public Shared Function GetCorrectPropertyName(Of T) _
             (ByVal expression As Expression(Of Func(Of T, Object))) As String
    If TypeOf expression.Body Is MemberExpression Then
        Return DirectCast(expression.Body, MemberExpression).Member.Name
    Else
        Dim op = (CType(expression.Body, UnaryExpression).Operand)
        Return DirectCast(op, MemberExpression).Member.Name
    End If
End Function
What's the System.Linq.Expressions.ExpressionVisitor.VisitExtension and the System.Linq.Expressions.ExpressionType.Exten

What's the System.Linq.Expressions.ExpressionVisitor.VisitExtension and the System.Linq.Expressions.ExpressionType.Exten


By : Reese Thompson
Date : March 29 2020, 07:55 AM
around this issue In this case, extension does not represent any kind of built-in syntax, but correspond to nodes that applications can define and assign arbitrary meaning to.
That concept is very useful when one manipulates Expression trees in an application, as these extension nodes can be fully integrated into what is otherwise a normal expression tree.
code :
from e in table where e.FirstKey == e.SecondKey select e;
from e in table where Key(e.FirstKey1, e.FirstKey2) == Key(e.SecondKey1, e.SecondKey2) select e;
from e in table where e.FirstKey1 == e.SecondKey1 && e.FirstKey2 == e.SecondKey2;
Cannot convert from 'System.Linq.Expressions.LambdaExpression' to 'System.Linq.Expressions.Expression

Cannot convert from 'System.Linq.Expressions.LambdaExpression' to 'System.Linq.Expressions.Expression


By : r00t
Date : March 29 2020, 07:55 AM
this will help It seems like you are trying to implement OrderBy dynamically using expression trees. You should try the following:
code :
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string sortProperty, ListSortDirection sortOrder)
{
    var type = typeof(T);
    var property = type.GetProperty(sortProperty);
    var parameter = Expression.Parameter(type, "p");
    var propertyAccess = Expression.MakeMemberAccess(parameter, property);
    var orderByExp = Expression.Lambda(propertyAccess, parameter);
    var typeArguments = new Type[] { type, property.PropertyType };
    var methodName = sortOrder == ListSortDirection.Ascending ? "OrderBy" : "OrderByDescending";
    var resultExp = Expression.Call(typeof(Queryable), methodName, typeArguments, source.Expression, Expression.Quote(orderByExp));
    return source.Provider.CreateQuery<T>(resultExp);
}
collection.OrderBy("Property on which you want to sort", ListSortDirection.Ascending);
Combing Array Inline - LINQ

Combing Array Inline - LINQ


By : samdelnaki
Date : March 29 2020, 07:55 AM
help you fix your problem You can use Concat:
code :
MyArray[] Arrayitems = SomeOtherList.Concat(SomeOtherListNo2)
.Select(x => new MyArray()
{
   ArrayPar1 = x.ListPar1,
}).ToArray();
MyArray[] Arrayitems = SomeOtherList.Union(SomeOtherListNo2)
.Select(x => new MyArray()
{
   ArrayPar1 = x.ListPar1,
}).ToArray();
Unable to cast object of type 'System.Linq.Expressions.FieldExpression' to type 'System.Linq.Expressions.ParameterExpres

Unable to cast object of type 'System.Linq.Expressions.FieldExpression' to type 'System.Linq.Expressions.ParameterExpres


By : Good Pen
Date : March 29 2020, 07:55 AM
help you fix your problem You should try calling Include method in the DbSet that you want to load the related entity:
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