I have the following code:
var aaData = myapi.GetData().AsEnumerable().Select(x => new {
Id = x["myID"],
Desc = x["myDesc"]
});
Trying to do the following
aaData = aaData.OrderBy((string.Join(",", request.Order
.Select(x => request.Columns[x.Column].Data + " " + x.Dir))));
Getting error:
CS0266 Cannot implicitly convert type 'System.Collections.Generic.IEnumerable<>' to 'System.Data.EnumerableRowCollection<>'. An explicit conversion exists (are you missing a cast?)
How to fix this?
GetData returns a DataTable
Request is an object having a property:
public OrderCol[] Order { get; set; }
OrderCol is
public class OrderCol {
public int Column { get; set; }
public string Dir { get; set; }
}
Thanks for your assistance.
The above code works for the case when I get a List<> back instead of DataTable. The error states that a Cast is needed and it seems to be how DataTable.AsEnumerable is set up as a EnumerableRowCollection
Can use a mock datatable to mimic the above
DataTable dt = new DataTable();
dt.clear();
dt.Columns.Add("myID");
dt.Columns.Add("myDesc");
all i needed was to convert to a list and things worked fine
I am building dynamic linq expressions which is working fine for a single entity.
For example:
I have a class called Employee and empeduinfo
public class Employee
{
public int Id { get; set; }
public string Name { get; set; }
}
public class EmpEduInfo
{
public int Id { get; set; }
public string Name { get; set; }
public int EmpId { get; set; }
}
I need to get all the the employees and empeduinfo class starts with "x"
I prepared expression for startswith("x")
var temp= entities.employees.Include("EmpEduInfo").Where(mydynamicexpression);
In this case it is filtering only parent table not on child.
I need to prepare generic expression so than i need to filter both parent and child objects dynamically.
Without using expression I know a solution:
var temp= (from ee in entities.Employee.Include("EmpEduInfo").Where(x => x.name.StartsWith("t"))
where ee.EmpEduInfo.Where(x => x.name.StartsWith("t")).Count()>0
select ee).ToList();
using expressions I am building generic expression to provide dynamic advance search rather than writing in each and every entity.
Here is my expression details
// Get the method information for the String.StartsWith() method
MethodInfo mi = typeof(string).GetMethod("StartsWith", new Type[] { typeof(string) });
// Build the parameter for the expression
ParameterExpression empparam= Expression.Parameter(typeof(employee), "ename");;
// Build the member that was specified for the expression
MemberExpression field = Expression.PropertyOrField(empparam, "name");
// Call the String.StartsWith() method on the member
MethodCallExpression startsWith = Expression.Call(field, mi, Expression.Constant("t"));
var namelamda = Expression.Lambda<Func<employee, bool>>(startsWith, new ParameterExpression[] { empparam });
var temp = entities.employees.Include("empedudetails").Where(namelamda).ToList();
You can look at the Expression the compiler generates using IQueryable:
IQueryable<Employee> query =
from ee in entities.Employee ...
var expression = query.Expression;
Look at expression in a debugger to see what you need to generate - LINQPad is good for this.
You might want to simplify your query a bit first:
IQueryable<Employee> query =
from ee in entities.Employee.Include("EmpEduInfo")
where
ee.name.StartsWith("t") &&
ee.EmpEduInfo.Any(x => x.name.StartsWith("t"))
select ee;
I was trying in EF 4.0 either we have write DB extentions for the same.
Option is provided in EF 4.1
http://www.asp.net/mvc/tutorials/getting-started-with-ef-using-mvc/reading-related-data-with-the-entity-framework-in-an-asp-net-mvc-application
Thanks.
I used Linq to Entity, for fetch a model from DB
var works = db.Work.Where(a => a.StartDate == DateTime.Now).ToList();
this model contain a DateTime that I want to change it to string before send it to view
beacuase need to show it as a persianDate Time,
like this :
foreach (var item in workslist)
{
item.StartDate = "1391/01/01"; //Just For Exapmle as you know this won't work
}
return View(workslist);
So is there any way to change a data type in a strongly typed model? or other way to do this except save DateTime as String in my DB
You can use the [DisplayFormat] attribute with EditorFor/DisplayFor helpers to format the data.
[DisplayFormat(ApplyFormatInEditMode = true, DataFormatString = "{0:yyyy/mm/dd}")]
public DateTime StartDate { get; set; }
Then in view:
#Html.EditorFor(m => m.StartDate)
OR, you can also consider to define separate ViewModel for your 'Work' domain model. Though this approach results in more code, it's provide more flexibility and considered as good practice.
Here is sample code:
public class Work
{
public DateTime StartDate {get;set;}
}
public class WorkViewModel
{
public WorkViewModel()
{
}
public string StartDate { get; set; }
public static WorkViewModel Map(Work domainModel)
{
return new WorkViewModel() {
//Apply your Date format logic
StartDate = domainModel.StartDate.ToString("yyyy/MM/dd")
};
}
}
In action method:
var works = db.Work.Where(a => a.StartDate == DateTime.Now).ToList();
var workViewModels = new List<WorkViewModel>(works.Count);
foreach (var work in works)
workViewModels.Add(WorkViewModel.Map(work));
return View(workViewModels);
you can have a function in your controller to change datetime to string
public string changeDateTimeToPersianString ( DateTime time)
{
// your code
}
then you can call this function from your View.
in Razor something like this
#changeDateTimeToPersianString(workslistitem.StartDate)
i'm quite new to Entity Framework (and asp.net mvc 3) and this is my really first experience with EF4.1 code first.
My question is simple: when I generate via model a new table for database I would like to make
Automatically add current datetime to a field when a new row is created.
Automatically update the field every time the field is updated.
Actually, the variable appears like:
[DisplayName("Data Modifica")]
[DataType(DataType.DateTime)]
[DisplayFormat(DataFormatString = "{0:d}")]
public DateTime DataModifica { get; set; }
I guess i could write something on "OnModelCreating" event of datacontext but I'm too new to already master this :)
Can someone help?
thanks in advance,
V.
That has nothing to do with creation of model. The "model" is description of your mapping between classes and database. OnModelCreating is used to modify mapping definition, not to modify data. It has nothing to do with data in the entity instance itself.
If you want automatic modification you can override SaveChanges:
public override int SaveChanges()
{
DateTime now = DateTime.Now;
foreach (var entity in ChangeTracker.Entries<YourEntityType>()
.Where(e => e.State == EntityState.Added || e.State == EntityState.Modified)
.Select(e => e.Entity))
{
entity.DateModifica = now; // set the date
}
return base.SaveChanges();
}
Why not define the property to be one with a backing field, which is initialized to the default value ?
private DateTime _dateOfRequest = DateTime.Today;
[Display(Name = "Date of Request"), DataType(DataType.Date)]
public System.DateTime DateOfRequest {
get { return _dateOfRequest; }
set { _dateOfRequest = value; }
}
I'm using Entity Framework 4.1 Code First. In my entity, I have three date/time properties:
public class MyEntity
{
[Key]
public Id { get; set; }
public DateTime FromDate { get; set; }
public DateTime ToDate { get; set; }
[NotMapped]
public DateTime? QueryDate { get; set; }
// and some other fields, of course
}
In the database, I always have the From/To dates populated. I query against them using a simple where clause. But in the result set, I want to include the date I queried for. I need to persist this for some other business logic to work.
I'm working on an extension method to do this, but I'm running into problems:
public static IQueryable<T> WhereDateInRange<T>(this IQueryable<T> queryable, DateTime queryDate) where T : MyEntity
{
// this part works fine
var newQueryable = queryable.Where(e => e.FromDate <= queryDate &&
e.ToDate >= queryDate);
// in theory, this is what I want to do
newQueryable = newQueryable.Select(e =>
{
e.QueryDate = queryDate;
return e;
});
return newQueryable;
}
This doesn't work. It works if I use an IEnumerable, but I want to keep it as IQueryable so everything runs on the database side, and this extention method can still be used in any part of another query. When it's IQueryable, I get a compile error of the following:
A lambda expression with a statement body cannot be converted to an expression tree
If this was SQL, I would just do something like this:
SELECT *, #QueryDate as QueryDate
FROM MyEntities
WHERE #QueryDate BETWEEN FromDate AND ToDate
So the question is, how can I transform the expression tree I already have to include this extra property assignment? I have looked into IQueryable.Expression and IQueryable.Provider.CreateQuery - there's a solution in there somewhere. Maybe an assignment expression can be appended to the existing expression tree? I'm not familiar enough with the expression tree methods to figure this out. Any ideas?
Example Usage
To clarify, the goal is to be able to perform something like this:
var entity = dataContext.Set<MyEntity>()
.WhereDateInRange(DateTime.Now)
.FirstOrDefault();
And have the DateTime.Now persisited into the QueryDate of the resulting row, WITHOUT having more than one row returned from the database query. (With the IEnumerable solution, multiple rows are returned before FirstOrDefault picks the row we want.)
Another Idea
I could go ahead and map QueryDate like a real field, and set its DatabaseGeneratedOption to Computed. But then I would need some way to inject the "#QueryDate as QueryDate" into the SQL created by EF's select statements. Since it's computed, EF won't try to provide values during update or insert. So how could I go about injecting custom SQL into the select statements?
Ladislav is absolutely right. But since you obviously want the second part of your question to be answered, here is how you can use Assign. This won't work with EF, though.
using System;
using System.Linq;
using System.Linq.Expressions;
namespace SO5639951
{
static class Program
{
static void Main()
{
AdventureWorks2008Entities c = new AdventureWorks2008Entities();
var data = c.Addresses.Select(p => p);
ParameterExpression value = Expression.Parameter(typeof(Address), "value");
ParameterExpression result = Expression.Parameter(typeof(Address), "result");
BlockExpression block = Expression.Block(
new[] { result },
Expression.Assign(Expression.Property(value, "AddressLine1"), Expression.Constant("X")),
Expression.Assign(result, value)
);
LambdaExpression lambdaExpression = Expression.Lambda<Func<Address, Address>>(block, value);
MethodCallExpression methodCallExpression =
Expression.Call(
typeof(Queryable),
"Select",
new[]{ typeof(Address),typeof(Address) } ,
new[] { data.Expression, Expression.Quote(lambdaExpression) });
var data2 = data.Provider.CreateQuery<Address>(methodCallExpression);
string result1 = data.ToList()[0].AddressLine1;
string result2 = data2.ToList()[0].AddressLine1;
}
}
}
Update 1
Here is the same code after some tweaking. I got rid of the "Block" expression, that EF choked on in the code above, to demonstrate with absolute clarity that it's "Assign" expression that EF does not support. Note that Assign works in principle with generic Expression trees, it is EF provider that does not support Assign.
using System;
using System.Linq;
using System.Linq.Expressions;
namespace SO5639951
{
static class Program
{
static void Main()
{
AdventureWorks2008Entities c = new AdventureWorks2008Entities();
IQueryable<Address> originalData = c.Addresses.AsQueryable();
Type anonType = new { a = new Address(), b = "" }.GetType();
ParameterExpression assignParameter = Expression.Parameter(typeof(Address), "value");
var assignExpression = Expression.New(
anonType.GetConstructor(new[] { typeof(Address), typeof(string) }),
assignParameter,
Expression.Assign(Expression.Property(assignParameter, "AddressLine1"), Expression.Constant("X")));
LambdaExpression lambdaAssignExpression = Expression.Lambda(assignExpression, assignParameter);
var assignData = originalData.Provider.CreateQuery(CreateSelectMethodCall(originalData, lambdaAssignExpression));
ParameterExpression selectParameter = Expression.Parameter(anonType, "value");
var selectExpression = Expression.Property(selectParameter, "a");
LambdaExpression lambdaSelectExpression = Expression.Lambda(selectExpression, selectParameter);
IQueryable<Address> finalData = assignData.Provider.CreateQuery<Address>(CreateSelectMethodCall(assignData, lambdaSelectExpression));
string result = finalData.ToList()[0].AddressLine1;
}
static MethodCallExpression CreateSelectMethodCall(IQueryable query, LambdaExpression expression)
{
Type[] typeArgs = new[] { query.ElementType, expression.Body.Type };
return Expression.Call(
typeof(Queryable),
"Select",
typeArgs,
new[] { query.Expression, Expression.Quote(expression) });
}
}
}
No, I don't think there is a solution. It is true that you can modify expression tree but you will get exactly the same exception as you got with your linq query because that query actually is what you will build in expression tree. The problem is not in expression tree but in the mapping. EF can't map QueryData to the result. Moreover you are trying to do projection. Projection can't be done to mapped entity and anonymous type can't be returned from the method.
You can off course do the select you mentioned but simply you can't map it to your entity. You must create a new type for that:
var query = from x in context.MyData
where x.FromDate <= queryDate && x.ToDate >= queryDate
select new MyDateWrapper
{
MyData = x,
QueryDate = queryDate
};
Automapper has Queryable Extensions, i think it can resolve your needs.
You can use ProjectTo to calculate property on runtime.
Ef Core 2 set value to ignored property on runtime
http://docs.automapper.org/en/stable/Queryable-Extensions.html
Example configuration:
configuration.CreateMap(typeof(MyEntity), typeof(MyEntity))
.ForMember(nameof(Entity.QueryDate), opt.MapFrom(src => DateTime.Now));
Usage:
queryable.ProjectTo<MyEntity>();
Thank you for all of the valuable feedback. It sounds like the answer is "no - you can't do it that way".
So - I figured out a workaround. This is very specific to my implementation, but it does the trick.
public class MyEntity
{
private DateTime? _queryDate;
[ThreadStatic]
internal static DateTime TempQueryDate;
[NotMapped]
public DateTime? QueryDate
{
get
{
if (_queryDate == null)
_queryDate = TempQueryDate;
return _queryDate;
}
}
...
}
public static IQueryable<T> WhereDateInRange<T>(this IQueryable<T> queryable, DateTime queryDate) where T : MyEntity
{
MyEntity.TempQueryDate = queryDate;
return queryable.Where(e => e.FromDate <= queryDate && e.ToDate >= queryDate);
}
The magic is that I'm using a thread static field to cache the query date so it's available later in the same thread. The fact that I get it back in the QueryDate's getter is specific to my needs.
Obviously this isn't an EF or LINQ solution to the original question, but it does accomplish the same effect by removing it from that world.