C# Reflection Expression Linq
I'm having some problems with C# dynamic generated lambda expressions.
Considering the following scenario:
public class Person {
public long Id { get; set; }
public string Name { get; set; }
}
List<Person> persons = new List<Person> () {
new Person { Id = 1, Name = "Foo" },
new Person { Id = 2, Name = "Bar" },
new Person { Id = 3, Name = "Baz" },
new Person { Id = 4, Name = null },
};
Now, doing the follow code
ParameterExpression param = Expression.Parameter(typeof(Person), "arg");
Expression prop = Expression.Property(param, "Name");
Expression value = Expression.Constant("bar");
Type type = prop.Type;
MethodInfo toLower = typeof(String).GetMethod("ToLower", Type.EmptyTypes);
Expression expLower = Expression.Call(prop, toLower);
Expression clausule = Expression.Call(expLower, type.GetMethod("Contains", new { type }), value);
Expression notNull = Expression.NotEqual(prop, Expression.Constant(null));
clausule = Expression.And(notNull, clausule);
var exp = Expression.Lambda<Func<T, bool>>(clausule, param);
The above code generate the following exp.
//arg => ((arg.Name != null) And (arg.Name.ToLower().Contains("bar")))
Now, trying to apply that to my list.
The filter below works
var filteredListThatWorks = persons.Where(arg => arg.Name != null && arg.Name.ToLower().Contains("bar")).ToList();
The one below throws exception of Null object ( because of Id 4 name)
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();
The same expression, when generated by lambda, throws exp, when manually inputed, works.
Anyone knows a way to solve that ?
Br,
c# lambda reflection
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
add a comment |
I'm having some problems with C# dynamic generated lambda expressions.
Considering the following scenario:
public class Person {
public long Id { get; set; }
public string Name { get; set; }
}
List<Person> persons = new List<Person> () {
new Person { Id = 1, Name = "Foo" },
new Person { Id = 2, Name = "Bar" },
new Person { Id = 3, Name = "Baz" },
new Person { Id = 4, Name = null },
};
Now, doing the follow code
ParameterExpression param = Expression.Parameter(typeof(Person), "arg");
Expression prop = Expression.Property(param, "Name");
Expression value = Expression.Constant("bar");
Type type = prop.Type;
MethodInfo toLower = typeof(String).GetMethod("ToLower", Type.EmptyTypes);
Expression expLower = Expression.Call(prop, toLower);
Expression clausule = Expression.Call(expLower, type.GetMethod("Contains", new { type }), value);
Expression notNull = Expression.NotEqual(prop, Expression.Constant(null));
clausule = Expression.And(notNull, clausule);
var exp = Expression.Lambda<Func<T, bool>>(clausule, param);
The above code generate the following exp.
//arg => ((arg.Name != null) And (arg.Name.ToLower().Contains("bar")))
Now, trying to apply that to my list.
The filter below works
var filteredListThatWorks = persons.Where(arg => arg.Name != null && arg.Name.ToLower().Contains("bar")).ToList();
The one below throws exception of Null object ( because of Id 4 name)
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();
The same expression, when generated by lambda, throws exp, when manually inputed, works.
Anyone knows a way to solve that ?
Br,
c# lambda reflection
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
1
also keep in mind - when you usevar filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps usepersons.AsQueryable().Where(...), which forces it to use the expression-tree API
– Marc Gravell♦
Nov 23 '18 at 10:49
add a comment |
I'm having some problems with C# dynamic generated lambda expressions.
Considering the following scenario:
public class Person {
public long Id { get; set; }
public string Name { get; set; }
}
List<Person> persons = new List<Person> () {
new Person { Id = 1, Name = "Foo" },
new Person { Id = 2, Name = "Bar" },
new Person { Id = 3, Name = "Baz" },
new Person { Id = 4, Name = null },
};
Now, doing the follow code
ParameterExpression param = Expression.Parameter(typeof(Person), "arg");
Expression prop = Expression.Property(param, "Name");
Expression value = Expression.Constant("bar");
Type type = prop.Type;
MethodInfo toLower = typeof(String).GetMethod("ToLower", Type.EmptyTypes);
Expression expLower = Expression.Call(prop, toLower);
Expression clausule = Expression.Call(expLower, type.GetMethod("Contains", new { type }), value);
Expression notNull = Expression.NotEqual(prop, Expression.Constant(null));
clausule = Expression.And(notNull, clausule);
var exp = Expression.Lambda<Func<T, bool>>(clausule, param);
The above code generate the following exp.
//arg => ((arg.Name != null) And (arg.Name.ToLower().Contains("bar")))
Now, trying to apply that to my list.
The filter below works
var filteredListThatWorks = persons.Where(arg => arg.Name != null && arg.Name.ToLower().Contains("bar")).ToList();
The one below throws exception of Null object ( because of Id 4 name)
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();
The same expression, when generated by lambda, throws exp, when manually inputed, works.
Anyone knows a way to solve that ?
Br,
c# lambda reflection
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
I'm having some problems with C# dynamic generated lambda expressions.
Considering the following scenario:
public class Person {
public long Id { get; set; }
public string Name { get; set; }
}
List<Person> persons = new List<Person> () {
new Person { Id = 1, Name = "Foo" },
new Person { Id = 2, Name = "Bar" },
new Person { Id = 3, Name = "Baz" },
new Person { Id = 4, Name = null },
};
Now, doing the follow code
ParameterExpression param = Expression.Parameter(typeof(Person), "arg");
Expression prop = Expression.Property(param, "Name");
Expression value = Expression.Constant("bar");
Type type = prop.Type;
MethodInfo toLower = typeof(String).GetMethod("ToLower", Type.EmptyTypes);
Expression expLower = Expression.Call(prop, toLower);
Expression clausule = Expression.Call(expLower, type.GetMethod("Contains", new { type }), value);
Expression notNull = Expression.NotEqual(prop, Expression.Constant(null));
clausule = Expression.And(notNull, clausule);
var exp = Expression.Lambda<Func<T, bool>>(clausule, param);
The above code generate the following exp.
//arg => ((arg.Name != null) And (arg.Name.ToLower().Contains("bar")))
Now, trying to apply that to my list.
The filter below works
var filteredListThatWorks = persons.Where(arg => arg.Name != null && arg.Name.ToLower().Contains("bar")).ToList();
The one below throws exception of Null object ( because of Id 4 name)
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();
The same expression, when generated by lambda, throws exp, when manually inputed, works.
Anyone knows a way to solve that ?
Br,
c# lambda reflection
c# lambda reflection
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
asked Nov 23 '18 at 10:38
Lucas FreitasLucas Freitas
4502928
4502928
1
also keep in mind - when you usevar filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps usepersons.AsQueryable().Where(...), which forces it to use the expression-tree API
– Marc Gravell♦
Nov 23 '18 at 10:49
add a comment |
1
also keep in mind - when you usevar filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps usepersons.AsQueryable().Where(...), which forces it to use the expression-tree API
– Marc Gravell♦
Nov 23 '18 at 10:49
1
1
also keep in mind - when you use
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps use persons.AsQueryable().Where(...), which forces it to use the expression-tree API– Marc Gravell♦
Nov 23 '18 at 10:49
also keep in mind - when you use
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps use persons.AsQueryable().Where(...), which forces it to use the expression-tree API– Marc Gravell♦
Nov 23 '18 at 10:49
add a comment |
1 Answer
1
active
oldest
votes
And is &; you want to use AndAlso (&&):
clausule = Expression.AndAlso(notNull, clausule);
When in doubt, sharplab.io is an excellent tool here; if I use:
Expression<Func<Person, bool>> filter
= arg => arg.Name != null && arg.Name.ToLower().Contains("bar");
it tells me that it compiles to be equivalent to:
// ...
BinaryExpression body = Expression.AndAlso(left, Expression.Call(instance, method, obj));
// ...
(note that it has to lie about some of the instructions though, as it compiles to things that can't actually be expressed in raw C#)
see it in action
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
add a comment |
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1 Answer
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active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
And is &; you want to use AndAlso (&&):
clausule = Expression.AndAlso(notNull, clausule);
When in doubt, sharplab.io is an excellent tool here; if I use:
Expression<Func<Person, bool>> filter
= arg => arg.Name != null && arg.Name.ToLower().Contains("bar");
it tells me that it compiles to be equivalent to:
// ...
BinaryExpression body = Expression.AndAlso(left, Expression.Call(instance, method, obj));
// ...
(note that it has to lie about some of the instructions though, as it compiles to things that can't actually be expressed in raw C#)
see it in action
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
add a comment |
And is &; you want to use AndAlso (&&):
clausule = Expression.AndAlso(notNull, clausule);
When in doubt, sharplab.io is an excellent tool here; if I use:
Expression<Func<Person, bool>> filter
= arg => arg.Name != null && arg.Name.ToLower().Contains("bar");
it tells me that it compiles to be equivalent to:
// ...
BinaryExpression body = Expression.AndAlso(left, Expression.Call(instance, method, obj));
// ...
(note that it has to lie about some of the instructions though, as it compiles to things that can't actually be expressed in raw C#)
see it in action
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
add a comment |
And is &; you want to use AndAlso (&&):
clausule = Expression.AndAlso(notNull, clausule);
When in doubt, sharplab.io is an excellent tool here; if I use:
Expression<Func<Person, bool>> filter
= arg => arg.Name != null && arg.Name.ToLower().Contains("bar");
it tells me that it compiles to be equivalent to:
// ...
BinaryExpression body = Expression.AndAlso(left, Expression.Call(instance, method, obj));
// ...
(note that it has to lie about some of the instructions though, as it compiles to things that can't actually be expressed in raw C#)
see it in action
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
And is &; you want to use AndAlso (&&):
clausule = Expression.AndAlso(notNull, clausule);
When in doubt, sharplab.io is an excellent tool here; if I use:
Expression<Func<Person, bool>> filter
= arg => arg.Name != null && arg.Name.ToLower().Contains("bar");
it tells me that it compiles to be equivalent to:
// ...
BinaryExpression body = Expression.AndAlso(left, Expression.Call(instance, method, obj));
// ...
(note that it has to lie about some of the instructions though, as it compiles to things that can't actually be expressed in raw C#)
see it in action
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
answered Nov 23 '18 at 10:43
Marc Gravell♦Marc Gravell
793k19821612565
793k19821612565
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
add a comment |
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
You deserve a cookie Sir! 4 more mins to mark as Correct. Thank you very much
– Lucas Freitas
Nov 23 '18 at 10:49
add a comment |
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1
also keep in mind - when you use
var filteredListThatGivesExp = persons.Where(exp.Compile()).ToList();, that is being compiled to a delegate, not an expression tree; if you want truly equivalent code, you should perhaps usepersons.AsQueryable().Where(...), which forces it to use the expression-tree API– Marc Gravell♦
Nov 23 '18 at 10:49