I want to retrieve a specific record using IQueryable. But i get error 'No generic method 'Where' on type 'System.Linq.Queryable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic.'. I got the selected row id, but I cannot display it out. Here is my code.
internal static IQueryable GetRecordsFromPrimaryKeys(this IQueryable datasource, List<FilterDescriptor> primaryKeys)
{
IQueryable data = datasource;
ParameterExpression paramExp = null;
bool firstLoop = false;
System.Linq.Expressions.Expression predicate = null;
var RecordType = datasource.GetObjectType();
paramExp = RecordType.Parameter();
foreach (FilterDescriptor primaryKey in primaryKeys)
{
if (!(firstLoop))
{
predicate = data.Predicate(paramExp, primaryKey.ColumnName, primaryKey.Value, FilterType.Equals, false, RecordType);
firstLoop = true;
}
else
{
predicate = predicate.AndPredicate(data.Predicate(paramExp, primaryKey.ColumnName, primaryKey.Value, FilterType.Equals, false, RecordType));
}
}
if (paramExp != null && predicate != null)
{
var lambda = Expression.Lambda(predicate, paramExp);
data = data.Provider.CreateQuery(
Expression.Call(
typeof(Queryable),
"Where",
new Type[] { data.ElementType },
data.Expression,
lambda
)
);
}
return data;
}
My Code works well for IEnumerable/IQueryable/ICollection . But it throws the exception when i specify the class with the keyword virtual and type as ICollection. My code is
public class RoomType
{
public int ID { get; set; }
[MaxLength(10, ErrorMessage = "Room code cannot be longer than 10 characters.")]
public string Code { get; set; }
[MaxLength(50, ErrorMessage = "Room name cannot be longer than 50 characters.")]
public string Name { get; set; }
public virtual ICollection<RoomCategory> RoomCategories { get; set; }
}
Some random values gets appended to 'RecordType' while using the keyword 'virtual'. I think this leads to the exception. Still searching for the solution.
I don't know what is going wrong . Any suggestions welcome.
Thanks.
I just ran into a similar situation. The problem stems from the fact that in some cases you're dealing with the "proxy" not the actual entity. So, you want to make sure that RecordType matches data.ElementType.
try:
var recordType = datasource.GetObjectType();
// make sure we have the correct type (not the proxy)
if (recordType.BaseType.Name != "Object")
recordType = recordType.BaseType;
Or better yet, try:
var recordType = data.ElementType
Try to use typeof(Enumerable) instead of typeof(Queryable)
Related
I'm just learning visual c# in visual studio
Ok, so I have a ton of data fields in a form, and then I want to write the handlers to all call one main method, update, which then updates a resultsEntry object, which encapsulates a bunch of uint variables with various names.
How do I write an update method to put in either the results object, or the update method that will take the name of the variable in resultsEntry as a string, and the integer to update it with, and then update that field.
Basically, I need to do a
resultsEntry.(inStringHere) = inValueHere;
where resultsEntry is the object being updated, the inStringHere specifies the field to be updated, and the inValueHere represents the integer value to assign to it.
Thanks!
Sam French
You have two challenges,
Setting a field/property in class using a string (the focus of your question). This will be accomplished using reflection.
Converting values to the type in your class (this may not be a problem for you, you may have 'typed' values. I have an ugly solution because this is not the main focus of your question.
Setting a property by name (see comments preceded with '**'):
static class Program
{
// A 'ResultEntry' type
public class ResultEntry
{
public int ID { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
}
static void Main()
{
// some tuples Field1 = Property Name; Field2 = Raw Value (string)
List<Tuple<string, string>> rawEntries = new List<Tuple<string, string>>() {
new Tuple<string,string>("ID", "1")
, new Tuple<string, string>("FirstName", "George")
, new Tuple<string, string>("LastName", "Washington")
};
ResultEntry resultEntry = new ResultEntry();
// ** Get MemberInfo's for your ResultEntry. Do this once, not for each instance of ResultEntry!
MemberInfo[] members = resultEntry.GetType().GetMembers(BindingFlags.Public | BindingFlags.Instance);
// Iterate over input
foreach (var raw in rawEntries)
{
// find a MemberInfo (PropertyInfo) that matches your input 'PropertyName'
MemberInfo member = members.FirstOrDefault(m => m.MemberType == MemberTypes.Property && m.Name == raw.Item1);
if (member != null)
{
// if you input is typed you will not have to deal with
// conversion of the string to the actual type of the property
object val = raw.Item2.MyConverter(((PropertyInfo)member).PropertyType);
// ** set the value in 'ResultEntry'
((PropertyInfo)member).SetValue(resultEntry, val, null);
}
}
Console.WriteLine(string.Format("Result Entry: ID = {0}, FirstName = {1}, LastName = {2}", resultEntry.ID, resultEntry.FirstName, resultEntry.LastName));
Console.ReadLine();
}
}
If you need to deal with converting raw string input to type (e.g. string to int), then is just one strategy...
public static class Extensions
{
public static object MyConverter(this string rawValue, Type convertToMe)
{
// ugly, there are other strategies
object val;
if (convertToMe == typeof(Int32))
val = Convert.ToInt32(rawValue);
// ... add other type conversions
else
val = rawValue;
return val;
}
}
Hope this helps.
I have been attempting to figure out why a Linq query that returns a list of U.S. States formatted for a drop down list will not cast to a List when the code returns to the calling method. The error that I get is:
Unable to cast object of type 'WhereSelectListIterator'2[StateListing.States,<>f__AnonymousTypea'2[System.String,System.String]]' to type 'System.Collections.Generic.List`1[StateListing.States]'
The namespace StateListing from the error, is a dll library that has a class called States returning an IEnumerable List of states shown below.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace StateListing
{
public class States
{
public string StateAbbriviation { get; set; }
public int StateID { get; set; }
public string StateName { get; set; }
static int cnt = 0;
public static IEnumerable<States> GetStates()
{
return new List<States>
{
new States
{
StateAbbriviation = "AL",
StateID=cnt++,
StateName = "Alabama"
},
new States
{
StateAbbriviation = "AL",
StateID=cnt++,
StateName = "Alaska"
}
//Continued on with the rest of states
}.AsQueryable();
}
}
}
In my control I make a call to GetStates that returns a List of States from the class library above.
[HttpPost]
public JsonResult GetStateOptions()
{
try
{
//Return a list of options for dropdown list
var states = propertyRepository.GetStates();
return Json(new { Result = "OK", options = states });
}
In the property repository class I have two methods one to get the StateList from the library, and another to format the listing of states for a drop down list in my view.
public List<States> GetStateList()
{
var items = (from s in States.GetStates()
select s).ToList();
return items;
}
List<States> IPropertyRepository.GetStates()
{
try
{
List<States> RawStates = GetStateList();
var stateList = RawStates.Select(c => new { DisplayText = c.StateName, Value = c.StateID.ToString() });
return (List<States>)stateList; //<=== Error
}
The error occurs when the code reaches the return within the GetStates method.
Any help with this casting problem explaining what I'm doing wrong would be appreciated.
This is the problem:
var stateList = RawStates.Select(c => new { DisplayText = c.StateName,
Value = c.StateID.ToString() });
return (List<States>)stateList;
Two issues:
Select doesn't return a List<T>
You're not= selecting States objects; you're selecting an anonymous type
The first is fixable using ToList(); the second is fixable either by changing your Select call or by changing your method's return type. It's not really clear what you really want to return, given that States doesn't have a DisplayText or Value property.
I would expect a method of GetStates to return the states - in which case you've already got GetStatesList() which presumably does what you want already.
Basically, you need to think about the type you really want to return, and make both your method return type and the method body match that.
You are projecting your LINQ query to an anonymmous object and not to a State list which obviously cannot work. The 2 types are incompatible. So start by modifying your repository layer and get rid of the GetStateList method:
public class PropertyRepository: IPropertyRepository
{
public List<States> GetStates()
{
return States.GetStates().ToList();
}
}
and then project to the desired structure in your controller:
[HttpPost]
public JsonResult GetStateOptions()
{
var states = propertyRepository.GetStateList();
var options = states.Select(x => new
{
DisplayText = c.StateName,
Value = c.StateID.ToString()
}).ToList();
return Json(new { Result = "OK", options = states });
}
I have pasted my entire test app below. It's fairly compact so I am hoping that it's not a problem. You should be able to simply cut and paste it into a console app and run it.
I need to be able to filter on any one or more of the Person objects' properties, and I don't know which one(s) until runtime. I know that this has beed discussed all over the place and I have looked into and am also using tools such as the PredicateBuilder & Dynamic Linq Library but the discussion aroung them tends to focus more on Sorting and ordering, and each have been struggling with their own issues when confronted with Nullable types. So I thought that I would attempt to build at least a supplemental filter that could address these particular scenarios.
In the example below I am trying to filter out the family members who were born after a certain date. The kick is that the DateOfBirth field on the objects being filterd is a DateTime property.
The latest error I am getting is
No coercion operator is defined between types 'System.String' and 'System.Nullable`1[System.DateTime]'.
Which is the problem. I have attempted several different means of casting and converting but to varying degrees of failure. Ultimately this will be applied against an EF database whcih has also balked at conversion methods such as DateTime.Parse(--).
Any assistence would be greatly appreciated!
using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
List<Person> people = new List<Person>();
people.Add(new Person { FirstName = "Bob", LastName = "Smith", DateOfBirth = DateTime.Parse("1969/01/21"), Weight=207 });
people.Add(new Person { FirstName = "Lisa", LastName = "Smith", DateOfBirth = DateTime.Parse("1974/05/09") });
people.Add(new Person { FirstName = "Jane", LastName = "Smith", DateOfBirth = DateTime.Parse("1999/05/09") });
people.Add(new Person { FirstName = "Lori", LastName = "Jones", DateOfBirth = DateTime.Parse("2002/10/21") });
people.Add(new Person { FirstName = "Patty", LastName = "Smith", DateOfBirth = DateTime.Parse("2012/03/11") });
people.Add(new Person { FirstName = "George", LastName = "Smith", DateOfBirth = DateTime.Parse("2013/06/18"), Weight=6 });
String filterField = "DateOfBirth";
String filterOper = "<=";
String filterValue = "2000/01/01";
var oldFamily = ApplyFilter<Person>(filterField, filterOper, filterValue);
var query = from p in people.AsQueryable().Where(oldFamily)
select p;
Console.ReadLine();
}
public static Expression<Func<T, bool>> ApplyFilter<T>(String filterField, String filterOper, String filterValue)
{
//
// Get the property that we are attempting to filter on. If it does not exist then throw an exception
System.Reflection.PropertyInfo prop = typeof(T).GetProperty(filterField);
if (prop == null)
throw new MissingMemberException(String.Format("{0} is not a member of {1}", filterField, typeof(T).ToString()));
Expression convertExpression = Expression.Convert(Expression.Constant(filterValue), prop.PropertyType);
ParameterExpression parameter = Expression.Parameter(prop.PropertyType, filterField);
ParameterExpression[] parameters = new ParameterExpression[] { parameter };
BinaryExpression body = Expression.LessThanOrEqual(parameter, convertExpression);
Expression<Func<T, bool>> predicate = Expression.Lambda<Func<T, bool>>(body, parameters);
return predicate;
}
}
public class Person
{
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime? DateOfBirth { get; set; }
string Nickname { get; set; }
public int? Weight { get; set; }
public Person() { }
public Person(string fName, string lName)
{
FirstName = fName;
LastName = lName;
}
}
}
Update: 2013/02/01
My thought was then to convert the Nullabe type to it's Non-Nullable type version. So in this case we want to convert the <Nullable>DateTime to a simple DateTime type. I added the following code block before the call Expression.Convert call to determine and capture the type of the Nullable value.
//
//
Type propType = prop.PropertyType;
//
// If the property is nullable we need to create the expression using a NON-Nullable version of the type.
// We will get this by parsing the type from the FullName of the type
if (prop.PropertyType.IsGenericType && prop.PropertyType.GetGenericTypeDefinition() == typeof(Nullable<>))
{
String typeName = prop.PropertyType.FullName;
Int32 startIdx = typeName.IndexOf("[[") + 2;
Int32 endIdx = typeName.IndexOf(",", startIdx);
String type = typeName.Substring(startIdx, (endIdx-startIdx));
propType = Type.GetType(type);
}
Expression convertExpression = Expression.Convert(Expression.Constant(filterValue), propType);
This actually worked in removing the Nullable-ness from the DateTime but resulted in the following Coercion error. I remain confused by this as I thought that the purpose of the "Expression.Convert" method was to do just this.
No coercion operator is defined between types 'System.String' and 'System.DateTime'.
Pushing on I explicitly parsed the value to a DateTime and plugged that into the mix ...
DateTime dt = DateTime.Parse(filterValue);
Expression convertExpression = Expression.Convert(Expression.Constant(dt), propType);
... which resulted in an exception that outpaces any knowledge I have of Expressions, Lambdas and their related ilk ...
ParameterExpression of type 'System.DateTime' cannot be used for delegate parameter of type 'ConsoleApplication1.Person'
I am not sure what's left to try.
The problem is that when generating binary expressions, the operands have to be of compatible types. If not, you need to perform a conversion on one (or both) until they are compatible.
Technically, you cannot compare a DateTime with a DateTime?, the compiler implicitly promotes one to the other which allows us to do our comparisons. Since the compiler is not the one generating the expression, we need to perform the conversion ourself.
I've tweaked your example to be more general (and working :D).
public static Expression<Func<TObject, bool>> ApplyFilter<TObject, TValue>(String filterField, FilterOperation filterOper, TValue filterValue)
{
var type = typeof(TObject);
ExpressionType operation;
if (type.GetProperty(filterField) == null && type.GetField(filterField) == null)
throw new MissingMemberException(type.Name, filterField);
if (!operationMap.TryGetValue(filterOper, out operation))
throw new ArgumentOutOfRangeException("filterOper", filterOper, "Invalid filter operation");
var parameter = Expression.Parameter(type);
var fieldAccess = Expression.PropertyOrField(parameter, filterField);
var value = Expression.Constant(filterValue, filterValue.GetType());
// let's perform the conversion only if we really need it
var converted = value.Type != fieldAccess.Type
? (Expression)Expression.Convert(value, fieldAccess.Type)
: (Expression)value;
var body = Expression.MakeBinary(operation, fieldAccess, converted);
var expr = Expression.Lambda<Func<TObject, bool>>(body, parameter);
return expr;
}
// to restrict the allowable range of operations
public enum FilterOperation
{
Equal,
NotEqual,
LessThan,
LessThanOrEqual,
GreaterThan,
GreaterThanOrEqual,
}
// we could have used reflection here instead since they have the same names
static Dictionary<FilterOperation, ExpressionType> operationMap = new Dictionary<FilterOperation, ExpressionType>
{
{ FilterOperation.Equal, ExpressionType.Equal },
{ FilterOperation.NotEqual, ExpressionType.NotEqual },
{ FilterOperation.LessThan, ExpressionType.LessThan },
{ FilterOperation.LessThanOrEqual, ExpressionType.LessThanOrEqual },
{ FilterOperation.GreaterThan, ExpressionType.GreaterThan },
{ FilterOperation.GreaterThanOrEqual, ExpressionType.GreaterThanOrEqual },
};
Then to use it:
var filterField = "DateOfBirth";
var filterOper = FilterOperation.LessThanOrEqual;
var filterValue = DateTime.Parse("2000/01/01"); // note this is an actual DateTime object
var oldFamily = ApplyFilter<Person>(filterField, filterOper, filterValue);
var query = from p in people.AsQueryable().Where(oldFamily)
select p;
I don't know if this will work as-is for all cases but it certainly works for this particular case.
If you interrogate your body variable, you can see that the body of the expression you're creating is essentially DateOfBirth <= '2000/01/01'.
While on the face this may seem correct, you are trying to assign that body to a function that takes a Person (that's what T would be in your example) and returns a bool. You need to alter your logic such that the body reflects the input as a Person object, accesses the DateOfBirth property on that instance of the Person, and then performs the comparison.
In other words, the body of your expression has to take a T, find the right property on it, and then compare.
MVC3, Entity Framework 4.1 Code first.
Working with 2 tables
Model:
public class UniversityMaster
{
[Key]
public string UniversityId { get; set; }
public string UniversityName { get; set; }
}
public class ProgramMaster
{
[Key]
public string ProgramId { get; set; }
public string ProgramName { get; set; }
public string UniversityId { get; set; }
public virtual UniversityMaster University { get; set; } // navigation property
}
Dynamic expression for sorting (just to avoid a switch case statement):
public virtual IQueryable< ProgramMaster > GetQueryableSort(string sortField="", string sortDirection="")
{
IQueryable<ProgramMaster> query = _dbSet;
ParameterExpression pe = Expression.Parameter(typeof(ProgramMaster), string.Empty);
MemberExpression property = Expression.PropertyOrField(pe, sortField);
//get a exception here if the sort field is of navigation property (University.UniversityName)
LambdaExpression lambda = Expression.Lambda(property, pe);
if (sortDirection == "ASC")
orderbydir = "OrderBy";
else
orderbydir = "OrderByDescending";
MethodCallExpression call = Expression.Call(typeof(Queryable),
orderbydir, new Type[] { typeof(TEntity), property.Type }, query.Expression, Expression.Quote(lambda));
var returnquery = (IOrderedQueryable<ProgramMaster>)query.Provider.CreateQuery< ProgramMaster >(call);
return returnquery;
}
The page is displaying a grid with two columns Program Name and University Name using webgrid. The sorting work fine for Program Name column, however fails if sorted by University Name as this property is in UniversityMaster and the Expression.PropertyOrField searches this property in ProgramMaster. Here is the exception:
University.UniversityName' is not a member of type 'App.Core.Model.ProgramMaster
My question is how I make this work for navigation properties of my model class.
Hope I was able explain the scenario. Any help is appreciated.
Well that's because the MemberExpression is trying to call a member named Univerty.UniversityName on the parameter. What you want to do is call a member named Univerity on the parameter, then call UniversityName on that. Effectively, you need to iteratively resolve the property names.
public virtual IQueryable< ProgramMaster > GetQueryableSort(string sortField = "", string sortDirection = "")
{
IQueryable<ProgramMaster> query = _dbSet;
var propertyNames = sortField.Split(".");
ParameterExpression pe = Expression.Parameter(typeof(ProgramMaster), string.Empty);
Expression property = pe;
foreach(var prop in propertyName)
{
property = Expression.PropertyOrField(property, prop);
}
LambdaExpression lambda = Expression.Lambda(property, pe);
if (sortDirection == "ASC")
orderbydir = "OrderBy";
else
orderbydir = "OrderByDescending";
MethodCallExpression call = Expression.Call(
typeof(Queryable),
orderbydir,
new Type[] { typeof(TEntity), property.Type },
query.Expression,
Expression.Quote(lambda));
var returnquery = (IOrderedQueryable<ProgramMaster>)query.Provider.CreateQuery<ProgramMaster>(call);
return returnquery;
}
Microsoft has a DynamicQueryable class which can be used to dynamically construct certain portions of a LINQ query using strings. With this you can say myQuery.OrderBy("University.UniversityName") and it will handle building the expression. The same library also supports dynamic construction of SELECT and WHERE clauses.
You can find a copy of the source as part of the excellent EntityFramework.Extended package by Loresoft. Microsoft's file is at https://github.com/loresoft/EntityFramework.Extended/blob/master/Source/EntityFramework.Extended/Dynamic/DynamicQueryable.cs
I'm building a rather large filter based on an SearchObject that has 50+ fields that can be searched.
Rather than building my where clause for each one of these individually I thought I'd use some slight of hand and try building custom attribute suppling the necessary information and then using reflection to build out each of my predicate statements (Using LinqKit btw). Trouble is, that the code finds the appropriate values in the reflection code and successfully builds a predicate for the property, but the "where" doesn't seem to actually generate and my query always returns 0 records.
The attribute is simple:
[AttributeUsage(AttributeTargets.Property, AllowMultiple=true)]
public class FilterAttribute: Attribute
{
public FilterType FilterType { get; set; } //enum{ Object, Database}
public string FilterPath { get; set; }
//var predicate = PredicateBuilder.False<Metadata>();
}
And this is my method that builds out the query:
public List<ETracker.Objects.Item> Search(Search SearchObject, int Page, int PageSize)
{
var predicate = PredicateBuilder.False<ETracker.Objects.Item>();
Type t = typeof(Search);
IEnumerable<PropertyInfo> pi = t.GetProperties();
string title = string.Empty;
foreach (var property in pi)
{
if (Attribute.IsDefined(property, typeof(FilterAttribute)))
{
var attrs = property.GetCustomAttributes(typeof(FilterAttribute),true);
var value = property.GetValue(SearchObject, null);
if (property.Name == "Title")
title = (string)value;
predicate.Or(a => GetPropertyVal(a, ((FilterAttribute)attrs[0]).FilterPath) == value);
}
}
var res = dataContext.GetAllItems().Take(1000)
.Where(a => SearchObject.Subcategories.Select(b => b.ID).ToArray().Contains(a.SubCategory.ID))
.Where(predicate);
return res.ToList();
}
The SearchObject is quite simple:
public class Search
{
public List<Item> Items { get; set; }
[Filter(FilterType = FilterType.Object, FilterPath = "Title")]
public string Title { get; set; }
...
}
Any suggestions will be greatly appreciated. I may well be going way the wrong direction and will take no offense if someone has a better alternative (or at least one that works)
You're not assigning your predicate anywhere. Change the line to this:
predicate = predicate.Or(a => GetPropertyVal(a, ((FilterAttribute)attrs[0]).FilterPath) == value);