Class ExpressionTypeChanger<T>

A class for traversing expressions and changing the type of a parameter from a type to another

This is used by the system for Linq expressions generated against an interface and replacing them to work against the actual class implementation of that interface

Inheritance
object
ExpressionVisitor
ExpressionTypeChanger<T>
Inherited Members
Namespace: LemonEdge.Utils
Assembly: LemonEdge.Utils.dll
Syntax
public class ExpressionTypeChanger<T> : ExpressionVisitor
Type Parameters
Name Description
T

The type for the original expression
Remarks

See https://stackoverflow.com/questions/14932779/how-to-change-a-type-in-an-expression-tree for more details

For example: 

public interface IMyItem
{
    int Value { get; set; }
}

public class MyItem : IMyItem
{
public int Value { get; set; }


public override string ToString() => Value.ToString();



}


public class Example
{
public IEnumerable<MyItem> ChangeType()
{
Expression<Func<IMyItem, bool>> expr = x => x.Value > 10;
var newExpr = ExpressionTypeChanger<IMyItem>.Change<MyItem>(expr);
var items = new List<MyItem>() { new MyItem() { Value = 5 }, new MyItem() { Value = 15 } };
return items.Where(newExpr.Compile());
}
}
Would return: 15

Methods

Change<TT>(Expression<Func<T, bool>>)

Converts an expression from one type to another

Declaration
public static Expression<Func<TT, bool>> Change<TT>(Expression<Func<T, bool>> expr) where TT : T
Parameters
Type Name Description
Expression<Func<T, bool>> expr

The original expression to change the type of
Returns
Type Description
Expression<Func<TT, bool>>

A new expression with the type replaced
Type Parameters
Name Description
TT

The type to convert the original expression into
Remarks

For example: 

public interface IMyItem
{
    int Value { get; set; }
}

public class MyItem : IMyItem
{
public int Value { get; set; }


public override string ToString() => Value.ToString();



}


public class Example
{
public IEnumerable<MyItem> ChangeType()
{
Expression<Func<IMyItem, bool>> expr = x => x.Value > 10;
var newExpr = ExpressionTypeChanger<IMyItem>.Change<MyItem>(expr);
var items = new List<MyItem>() { new MyItem() { Value = 5 }, new MyItem() { Value = 15 } };
return items.Where(newExpr.Compile());
}
}
Would return: 15

VisitMember(MemberExpression)

This method is required because PersonData does not implement IPerson and it finds property in PersonData with the same name as the one referenced in expression and declared on IPerson

Declaration
protected override Expression VisitMember(MemberExpression node)
Parameters
Type Name Description
MemberExpression node
Returns
Type Description
Expression
Overrides

VisitParameter(ParameterExpression)

This method replaces original parameter with given in constructor

Declaration
protected override Expression VisitParameter(ParameterExpression node)
Parameters
Type Name Description
ParameterExpression node
Returns
Type Description
Expression
Overrides

Extension Methods