I would like to change the following code so as to handle grouping of more than 1 property
private Expression<Func<ProfileResultView, string>> DynamicGroupBy(string propertyName)
{
var parameterExp = Expression.Parameter(typeof(ProfileResultView), "x");
var memberExp = Expression.PropertyOrField(parameterExp, propertyName);
return Expression.Lambda<Func<ProfileResultView, string>>(memberExp, parameterExp);
}
so then this would be translated to
GroupBy(x => new { x.Column1, x.Column2 })
how can I write the anonymous type in the expression-tree syntax?
If the type of the grouping key does not matter for you, you can create types dynamically and call the grouping based on those types:
public static Expression<Func<TSource, object>> DynamicGroupBy<TSource>
(params string[] properties)
{
var entityType = typeof(TSource);
var props = properties.Select(x => entityType.GetProperty(x)).ToList();
var source = Expression.Parameter(entityType, "x");
// create x=> new myType{ prop1 = x.prop1,...}
var newType = CreateNewType(props);
var binding = props.Select(p => Expression.Bind(newType.GetField(p.Name),
Expression.Property(source, p.Name))).ToList();
var body = Expression.MemberInit(Expression.New(newType), binding);
var selector = Expression.Lambda<Func<TSource, object>>(body, source);
return selector;
}
public static Type CreateNewType(List<PropertyInfo> props)
{
AssemblyName asmName = new AssemblyName("MyAsm");
AssemblyBuilder dynamicAssembly = AssemblyBuilder
.DefineDynamicAssembly(asmName, AssemblyBuilderAccess.Run);
ModuleBuilder dynamicModule = dynamicAssembly.DefineDynamicModule("MyAsm");
TypeBuilder dynamicAnonymousType = dynamicModule
.DefineType("MyType", TypeAttributes.Public);
foreach (var p in props)
{
dynamicAnonymousType.DefineField(p.Name, p.PropertyType, FieldAttributes.Public);
}
return dynamicAnonymousType.CreateType();
}
Note that the group key type is object.
Related
I want to populate the itemsource of a ComboBox with items from my List, depending on which property from T is selected.
The statement should be like:
foreach property which is a string,
select the values of the property, make distinct.
public Dictionary<string, List<string>> CreateSuggestionsLists<T>(List<T> data)
{
var queryableData = data.AsQueryable();
var paramExp = Expression.Parameter(typeof(T), "left");
foreach (var pi in typeof(T).GetProperties().Where(p => p.PropertyType == typeof(string)))
{
var callExpr = Expression.MakeMemberAccess(paramExp, pi);
var lambdaExpr = Expression.Lambda(callExpr) ;
// From here on it goes wrong!!!
var comleteExpr = lambdaExpr as Expression<Func<T, bool>>;
var compiledExpr = comleteExpr.Compile();
var res = data.Select(compiledExpr).Distinct().ToList();
// add to results ...
}
return null;
}
The problem seems to be the casting from the lambda expression to prepare for compilation.
Thank you for your help.
First of all you need to provide paramExp to lambda. Secondly there is generic version of Lamda method which is just easier to use. Finally, you don't need to compile expression when you use IQueryable. You created queryableData variable and didn't use it.
Here is code:
public Dictionary<string, List<string>> CreateSuggestionsLists<T>(List<T> data)
{
var queryableData = data.AsQueryable();
var paramExp = Expression.Parameter(typeof(T), "left");
foreach (var pi in typeof(T).GetProperties().Where(p => p.PropertyType == typeof(string)))
{
var callExpr = Expression.MakeMemberAccess(paramExp, pi);
var lambdaExpr = Expression.Lambda<Func<T, bool>>(callExpr, paramExp);
var res = queryableData.Select(lambdaExpr).Distinct().ToList();
// add to results ...
}
return null;
}
I think you should check if the casting result is not null :
public Dictionary<string, List<string>> CreateSuggestionsLists<T>(List<T> data)
{
IQueryable<T> queryableData = data.AsQueryable();
ParameterExpression paramExp = Expression.Parameter(typeof(T), "left");
foreach (PropertyInfo pi in typeof(T).GetProperties().Where(p => p.PropertyType == typeof(string)))
{
MemberExpression callExpr = Expression.MakeMemberAccess(paramExp, pi);
LambdaExpression lambdaExpr = Expression.Lambda(callExpr);
// From here on it goes wrong!!!
if (!(lambdaExpr is Expression<Func<T, bool>> comleteExpr)) continue;
Func<T, bool> compiledExpr = comleteExpr.Compile();
List<bool> res = data.Select(compiledExpr).Distinct().ToList();
// add to results ...
}
return null;
}
I am creating a delegate for a Select statement in LINQ. Some of the property bindings are to child properties on the object I'm selecting from.
This is the LINQ statement I want to put in my delegate:
var list = dataSet.Select(x => new ViewModel()
{
Name = x.Name,
ClassType = x.ClassType.Description
};
I can get the Name no worries with my code, but I do not know how to get the ClassType.Description.
Here is my current code:
protected Func<Student, ManagerStudentListViewModel> GetSelectStatement()
{
var studentType = typeof(Student);
var viewModelType = typeof(ManagerStudentListViewModel);
var parameterExpression = Expression.Parameter(studentType, "x");
var newInstantiationExpression = Expression.New(viewModelType);
// Name Binding
var viewModelProperty = viewModelType.GetProperty("Name");
var studentProperty = studentType.GetProperty("Name");
var nameMemberExpression = Expression.Property(parameterExpression, studentProperty);
var nameBinding = Expression.Bind(viewModelProperty, nameMemberExpression);
// ClassType.Description Binding
// ???
var bindings = new List<MemberAssignment>() { nameBinding, classTypeBinding };
var memberInitExpression = Expression.MemberInit(newInstantiationExpression, bindings);
var lambda = Expression.Lambda<Func<Student, ManagerStudentListViewModel>>(memberInitExpression, parameterExpression);
return lambda.Compile();
}
Accessing deeply nested members is no different than accessing any other properties, provided you know the name of the members. Just create an expression to get the first property, then add the expression to get the second.
Expression<Func<Student, ManagerStudentListViewModel>> GetSelectStatement()
{
var studentType = typeof(Student);
var viewModelType = typeof(ManagerStudentListViewModel);
var param = Expression.Parameter(studentType, "x");
var nameValue = Expression.Property(param, "Name");
var classTypeValue = Expression.Property(
Expression.Property(param, "ClassType"), // get the class type
"Description"); // get the description of the class type
var nameMemberBinding = Expression.Bind(
viewModelType.GetProperty("Name"),
nameValue);
var classTypeMemberBinding = Expression.Bind(
viewModelType.GetProperty("ClassType"),
classTypeValue);
var initializer = Expression.MemberInit(
Expression.New(viewModelType),
nameMemberBinding,
classTypeMemberBinding);
return Expression.Lambda<Func<Student, ManagerStudentListViewModel>>(initializer, param);
}
I'm trying to make a helper method that creates a dynamic selector using expression tree.
The objective would be converting this selector into an expression tree.
var list = new User[0].AsQueryable();
var q = list.Select(u => new { User = u, Address = "Address X", Fax = "Fax Y" });
In the expression tree visualizer it shows something like:
Here is what I have tried so far:
var userParam = Expression.Parameter(typeof(User), "u");
var obj = new { User = new User(), Address = string.Empty, Fax = string.Empty };
var q = list.Select(DynamicSelect(obj, userParam));
static Expression<Func<User, T>> DynamicSelect<T>(T obj, ParameterExpression userParam)
{
var user = Expression.Lambda<Func<User, User>>(/* ?? stuck here */, userParam);
var newExpression = Expression.New(
typeof(T).GetConstructor(new []{typeof(User), typeof(string), typeof(string)}),
user,
Expression.Constant("Address X"),
Expression.Constant("Fax Y"),
);
return Expression.Lambda<Func<User, T>>(newExpression, userParam);
}
You don't need a lambda inside a lambda here, you can just use userParam directly:
static Expression<Func<User, T>> DynamicSelect<T>(T obj, ParameterExpression userParam)
{
var newExpression = Expression.New(
typeof(T).GetConstructor(new []{typeof(User), typeof(string), typeof(string)}),
userParam,
Expression.Constant("Address X"),
Expression.Constant("Fax Y"),
);
return Expression.Lambda<Func<User, T>>(newExpression, userParam);
}
Also, I don't understand why is userParam a parameter of the method, I would create it inside the method.
Im trying to implement Dynamic LINQ Query for selected columns to show has Output columns in LINQ Query.
Here is the error:
/Property 'System.String CompanyCode' is not defined for type
'System.String'"
public static void SelectProjection()
{
DataMovementDataContext dbMovement = new DataMovementDataContext();
var entity = dbMovement.ListofAccountingDocs2_1075s.AsQueryable();
Type type = entity.ElementType;
var entityParam = Expression.Parameter(entity.ElementType, "row");
Expression expr = entityParam;
string[] props = "AccountingDocumentNbr,CompanyCode,FiscalYearNbr".Split(',');
foreach (string prop in props)
{
// use reflection (not ComponentModel) to mirror LINQ
PropertyInfo pi = type.GetProperty(prop);
expr = Expression.Property(expr, pi);
type = pi.PropertyType;
}
// row => row.Property
// var columnLambda = Expression.Lambda( Expression.Property(entityParam, "GLCompanyCode"), entityParam);
var columnLambda = Expression.Lambda(Expression.Property(expr, "AccountingDocumentNbr,GLCompanyCode"), entityParam);
// Items.Select(row => row.Property)
var selectCall = Expression.Call(typeof(Queryable), "Select", new Type[] { entity.ElementType, columnLambda.Body.Type }, entity.Expression, columnLambda);
// Items.Select(row => row.Property).Distinct
var distinctCall = Expression.Call(typeof(Queryable), "Distinct", new Type[] { typeof(string) }, selectCall);
// colvalue => colvalue
var sortParam = Expression.Parameter(typeof(string), "AccountingDocumentNbr");
var columnResultLambda = Expression.Lambda(sortParam, sortParam);
// Items.Select(row => row.Property).Distinct.OrderBy(colvalue => colvalue)
var ordercall = Expression.Call(typeof(Queryable), "OrderBy",
new Type[] { typeof(string), columnResultLambda.Body.Type },
distinctCall, columnResultLambda);
var result = entity.Provider.CreateQuery(ordercall);
foreach (var item in result)
{
Console.Write(item);
}
}
Can any one provide me help in solving above error?
If we look at this code:
// I chnaged this part:
string[] props = new string[]
{
"AccountingDocumentNbr",
"CompanyCode",
"FiscalYearNbr"
};
Expression expr;
Type type = entity.ElementType;
foreach (string prop in props)
{
PropertyInfo pi = type.GetProperty(prop);
expr = Expression.Property(expr, pi);
type = pi.PropertyType; // This line may cause your loop
// to do something you dont want to do?
}
It seems to me that your loop going down the properties, gets a string and then searches for a prop called CompanyCode, which the class String obviously doesnt have.
Your loop does the following at the moment:
from type get the property named AccountingDocumentNbr
from the return type of property AccountingDocumentNbr get the property called CompanyCode
form the return type of property CompanyCode get the type of the property called FiscalYearNbr
I hardly doubt this is what you really want to do.
I have this bit of code as an example, basically it spits out
p => p.fieldname.StartsWith("123")
But who would i expand on this to do something like this:
p => p.anotherentity.fieldname.StartsWith("123")
Here is a sample of the code i am have refactored for own needs:
string propertyName = "FirstName";
string methodName = "StartsWith";
string keyword = "123";
Type t = typeof (Person);
ParameterExpression paramExp = Expression.Parameter(t, "p");
// the parameter: p
MemberExpression memberExp = Expression.MakeMemberAccess(paramExp,
t.GetMember(propertyName).FirstOrDefault());
// part of the body: p.FirstName
MethodCallExpression callExp = Expression.Call(memberExp,
typeof (string).GetMethod(methodName,
new Type[] {typeof (string)}),
Expression.Constant(keyword));
// the body: p.FirstName.StartsWith("123")
Expression<Func<Person, bool>> whereExp = Expression.Lambda<Func<Person, bool>>(callExp, paramExp);
Expression<Func<Person, string>> selectExp = Expression.Lambda<Func<Person, string>>(memberExp, paramExp);
Console.WriteLine(whereExp); // p => p.FirstName.StartsWith("123")
Console.WriteLine(selectExp); // p => p.FirstName
To further explain let me show you what i would like to do:
public class Person
{
public string IdentityCode {get;set;}
public Loans Loans {get;set;}
}
public class Loans
{
public int Id {get;set;}
public Asset Assets {get;set;}
public Person person {get;set;}
}
public class Asset
{
public string SerialNumber {get;set;}
}
Then using an expression build something like this:
p => p.Loans.Asset.SerialNumber.StartsWith("123)
Or
p => p.Loans.Person.IdentityCode.StartsWith("123")
untested, but...
ParameterExpression paramExp = Expression.Parameter(t, "p"); // the parameter: p
MemberExpression memberExp =
Expression.MakeMemberAccess(paramExp, t.GetMember(propertyName).FirstOrDefault());
would become something like:
ParameterExpression paramExp = Expression.Parameter(t, "p"); // the parameter: p
MemberExpression otherEntityExp =
Expression.MakeMemberAccess(paramExp, t.GetMember("anotherentity").FirstOrDefault());
MemberExpression memberExp =
Expression.MakeMemberAccess(otherEntityExp, t.GetMember(propertyName).FirstOrDefault());
I'm not sure what you're asking for, updating an expression or building one from scratch...
If you already have the existing, old expression and want to update it, it would be very easy to create a new one. The idea is to dig through the expression tree down to the expression you want to replace. Then update all parent expressions with the newly replaced one.
Expression<Func<Obj, bool>> expr = p => p.fieldname.StartsWith("123");
var body = expr.Body as MethodCallExpression; // *.StartsWith()
var obj = body.Object as MemberExpression; // p.fieldname
var param = expr.Parameters.First(); // p
var newAccess = Expression.PropertyOrField(param, "anotherentity"); // p.anotherentity
var newObj = obj.Update(newAccess); // update obj
var newBody = body.Update(newObj, body.Arguments); // update body
var newExpr = expr.Update(newBody, expr.Parameters);// update expr
Otherwise to build up the expression tree:
Expression<Func<Person, bool>> expr =
p => p.Loans.Asset.SerialNumber.StartsWith("123");
Work it out from the beginning.
var p = Expression.Parameter(typeof(Person), "p");
var accessLoans = Expression.PropertyOrField(p, "Loans");
var accessAsset = Expression.PropertyOrField(accessLoans, "Asset");
var accessSerialNumber = Expression.PropertyOrField(accessAsset, "SerialNumber");
var callArgs = new Expression[] { Expression.Constant("123", typeof(string)) };
var callStartsWith = Expression.Call(accessSerialNumber, "StartsWith", null, callArgs);
var newExpr = Expression.Lambda<Func<Person, bool>>(callStartsWith, p);
I'll leave the last one as an exercise for you.