I have struggle with adding the grouped data table with linq query to model property.
Here's my model
public class Ports
{
public String city { get; set; }
}
and here's my controller
public ActionResult ShipSchedule()
{
DatabaseContext db = new DatabaseContext();
var Ports = new Ports();
Ports.city = from m in db.ports_data group m by new { m.city } into n select new { n.Key.city };
return View();
}
I've replaced the model part to List<> and replaced again to another, but this part
Ports.city = (from m in db.ports_data group m by new { m.city } into n select new { newcity = n.Key.city }).ToList();
is still tell me that part cannot convert type 'system.collections.generic.list<<anonymous type: string newcity>>' to 'system.collections.generic.list<string>'
Did anyone know the correct ways from this?
and one more thing, I want to display that part to my view in dropdown, if anyone have a better ways
here's my view
#model example.Models.Ports
#{
List<SelectListItem> listItems = new List<SelectListItem>();
foreach (var mod in Model.city)
{
listItems.Add(new SelectListItem
{
Text = mod.ToString(),
Value = mod.ToString()
});
}
}
#Html.DropDownListFor(model => model.selected, listItems, "-- Select item --")
the error is telling you exactly what is wrong, you have a string but are trying to assign a list to it (two very different objects), you can simply:
public class Ports
{
public List<String> cities { get; set; }
}
which will make that string be valid, but a better practice would be make "Ports" a list and use it as List<Port> and each port will contain "city" (and all the other port properties).
but in any case to get all ports from the database you probably can do:
var ports = db.ports_data.ToList();
that should give you a list with all the ports in your database (no need to create that New Ports() and populate it, if you need to group by city it should be as easy as:
var ports = db.ports_data.GroupBy(x=>x.city).ToList();
in the comment you mentioned that you are getting duplicates, for that you may need distinct, but if you don't need duplicates you shouldn't be adding duplicates to the database to start with, so we would be touching the wrong end here, but in any case I believe you need Distinct() if combined with a select you will get only cities, different ones if there is duplicates:
var portsCities = db.ports_data.Select(x=>x.city).Distinct().ToList();
that will result in a List<string> of cities, all different
as you can see Linq have many ways to get exactly the data you need, I would play around with it and experiment, best way to learn!
I would also try to use LINQ method (as the examples above) if you are starting, it is easier to manage (more object oriented) you can see some examples here
Related
Using EF Core
We are trying to obtain all information of an assessment, which includes its groups and all assigned users. See the
Database Diagram
What is working in following order;
HttpPost (api/Assessment/aID/groups) of an empty group to an assessment
HttpPost (api/Group/gID/users) of users to an existing group
What we are trying to accomplish (code referenced is a different example, yet same principle);
HttpPost (api/Assessment/aID/groups) where a group already contains a list of users. When trying to accomplish this, a possible object cycle was detected which is not supported.
This piece of code is currently throwing a NullReference on Address
-------------------------------------------------------------------
Group groupToCreate = new Group { Name = dto.Name, Description = dto.Description };
foreach (var u in dto.Users)
{
groupToCreate.AddUser(new User
{
Name = u.Name,
Email = u.Email,
Address = new Address
{
Country = u.Address.Country,
City = u.Address.City,
PostalCode = u.Address.PostalCode,
Street = u.Address.Street,
HouseNr = u.Address.HouseNr,
BusNr = u.Address.BusNr
}
});
}
_groupRepository.Add(groupToCreate);
_groupRepository.SaveChanges();
return groupToCreate;
HttpGet (api/Assessment) which displays its assigned groups and linked users.
This seems to be working
------------------------
groupList = _groups.Select(g => new GroupDTO
{
Name = g.Name,
Description = g.Description,
Users = g.GroupUsers.Select(u => new UserDTO
{
Name = u.User.Name,
Email = u.User.Email,
Address = new AddressDTO
{
Country = u.User.Address.Country,
City = u.User.Address.City,
PostalCode = u.User.Address.PostalCode,
Street = u.User.Address.Street,
HouseNr = u.User.Address.HouseNr,
BusNr = u.User.Address.BusNr
}
}).ToList()
}).ToList();
References:
User
Group
Assessment
AssessmentRepo
Hard to tell with the details you're providing, but I'm guessing this is due to Having two-way navigation properties? Are you using EF here?
For example, if your User has a Navigation property allowing access to the user's Group, but a Group has a collection of User objects, then each of those users would themselves have the Group expressed within them... then when trying to express this it could easily get stuck in a cycle, e.g. a user would look like:
{
"Name":"user name",
"Group":{
"Name":"group1",
"Users":[
{
"Name":"user name",
"Group":{
"Name":"group1",
"Users":{
....
}
}
}
]
}
}
.. because a User has a Group, and the Group has a list of User objects, and each one of those has a Group... etc.
This is the sort of issue that comes from mixing your Data layer and DTO objects. Change your system so the objects returned by your REST methods are new objects designed for the requirements of the API/front-end. These objects may look very similar to your DB models (at least initially) but they should not be the same objects.
Create entirely new objects which don't have any logic or navigation properties, and exist only to pass information back to API consumers. For example, a simple class to give a list of user groups and the users in those groups may be defined as:
public class UserDto
{
public string UserName { get; set; }
public IEnumerable<string> Groups { get; set; }
}
public class UserListDto
{
public IEnumerable<UserDto> Users { get; set; }
}
And then your controller action could do something like:
var users = userService.GetAllUsers();
var result = new UserListDto {
Users = users.Select(u => new UserDto{
UserName = u.Name,
Groups = u.Groups.Select(g => g.Name)
}
};
return Ok(result);
..So the thing being serialised for the response doesn't have any complicated relationships to negotiate, and more importantly a change to how you are internally storing and working with the data won't affect the external contract of your API - API consumers can continue to see exactly the same information but how you store and compile this can change drastically.
It is tempting to think "The Data I need to return is basically the same as how I store it internally, so just re-use these classes" but that's not a great idea & will only ever give problems in the long run.
To avoid having to (re-)write a lot of code to 'convert' one object into another, I'd recommend looking into something like AutoMapper as this can make that fairly easily re-usable & allow you to put all this 'Translation' stuff into one place.
i know it is not complicated but i struggle with it.
I have IList<Material> collection
public class Material
{
public string Number { get; set; }
public decimal? Value { get; set; }
}
materials = new List<Material>();
materials.Add(new Material { Number = 111 });
materials.Add(new Material { Number = 222 });
And i have DbSet<Material> collection
with columns Number and ValueColumn
I need to update IList<Material> Value property based on DbSet<Material> collection but with following conditions
Only one query request into database
The returned data from database has to be limited by Number identifier (do not load whole database table into memory)
I tried following (based on my previous question)
Working solution 1, but download whole table into memory (monitored in sql server profiler).
var result = (
from db_m in db.Material
join m in model.Materials
on db_m.Number.ToString() equals m.Number
select new
{
db_m.Number,
db_m.Value
}
).ToList();
model.Materials.ToList().ForEach(m => m.Value= result.SingleOrDefault(db_m => db_m.Number.ToString() == m.Number).Value);
Working solution 2, but it execute query for each item in the collection.
model.Materials.ToList().ForEach(m => m.Value= db.Material.FirstOrDefault(db_m => db_m.Number.ToString() == m.Number).Value);
Incompletely solution, where i tried to use contains method
// I am trying to get new filtered collection from database, which i will iterate after.
var result = db.Material
.Where(x=>
// here is the reasonable error: cannot convert int into Material class, but i do not know how to solve this.
model.Materials.Contains(x.Number)
)
.Select(material => new Material { Number = material.Number.ToString(), Value = material.Value});
Any idea ? For me it is much easier to execute stored procedure with comma separated id values as a parameter and get the data directly, but i want to master linq too.
I'd do something like this without trying to get too cute :
var numbersToFilterby = model.Materials.Select(m => m.Number).ToArray();
...
var result = from db_m in db.Material where numbersToFilterBy.Contains(db_m.Number) select new { ... }
I am trying, to no avail to display a dropdown list of all units a user doesnt already have. So i have List A with all Units and List B with all Units the user has. What i want is List C which is basically List A with List B removed from it. I have so far managed to filter out the data but i cant seem to display it in my View. All i get is a blank dropdown list. Can anyone see where im going wrong??
public ActionResult AddUnit(String usrCode)
{
var units = unitsClient.GetAllunits();
var allunitsCode = (from s in units select s.unitCode).ToList();
var thisUnitCode = (from s in db.Units
where s.UsrCode == usrCode
select s.UnitCode).ToList();
var notGot = allunitsCode.Except(thisUnitCode);
List<unitsummaryDTO> list = UnitList(units, notGot);
ViewBag.unitCode = new SelectList(list, "unitCode", "unitTitle");
var model = new UserUnit { UsrCode = usrCode };
return View("AddUnit", model);
}
private List<unitsummaryDTO> UnitList(unitsService.unitsDTO[] units, IEnumerable<string> notGot)
{
var allunits = unitsClient.GetAllunits();
var allunitsCode = (from s in allunits select s.unitCode).ToList();
IEnumerable<String> list1 = allunitsCode;
IEnumerable<String> list2 = notGot;
var listFinal = list1.Union(list2).toList;
return listFinal.Select(x => new unitsummaryDTO(){unitCode = x}).ToList();
}
This is my View model. But all i get is a blank drop down?? Can anyone help me out.
#model Projv1.UserUnit
#Html.HiddenFor(model => model.unitCode)
#Html.DropDownList("UnitCode")
It would be blank because #Html.DropDownList("UnitCode") doesn't have a source. If you look at MSDN for Html.DropDownList, the one your most likely trying to use is DropDownList(String, IEnumerable<SelectListItem>).
Your putting your select list into the ViewBag as unitCode so try:
#Html.DropDownList("Unit Code", ViewBag.unitCode);
A much easier way of handling this is to extend UserUnit as a ViewModel (or create something) to have the items needed by the SelectList on it and let MVC do the heavy lifting in the binding.
public class UserUnit
{
// ... other properties
IEnumerable<unitsummaryDTO> UnitCodes { get; set; }
public string MyUnitCode { get; set; }
}
Then
#Html.DropDownListFor(n => n.MyUnitCode,
new SelectList(Model.UnitCodes, "unitCode", "unitTitle"))
In the following code that returns a list:
public List<Customer> GeAllCust()
{
var results = db.Customers
.Select(x => new { x.CustName, x.CustEmail, x.CustAddress, x.CustContactNo })
.ToList()
return results;
}
I get an error reporting that C# can't convert the list:
Error: Cannot implicitly convert type System.Collections.Generic.List<AnonymousType#1> to System.Collections.Generic.List<WebApplication2.Customer>
Why is that?
Here's a screenshot showing some additional information that Visual Studio provides in a tooltip for the error:
Is it right way to return some columns instead of whole table....?
public object GeAllCust()
{
var results = db.Customers.Select(x => new { x.CustName, x.CustEmail, x.CustAddress, x.CustContactNo }).ToList();
return results;
}
When you look the code:
x => new { ... }
This creates a new anonymous type. If you don't need to pull back only a particular set of columns, you can just do the following:
return db.Customers.ToList();
This assumes that Customers is an IEnumerable<Customer>, which should match up with what you are trying to return.
Edit
You have noted that you only want to return a certain subset of columns. If you want any sort of compiler help when coding this, you need to make a custom class to hold the values:
public class CustomerMinInfo
{
public string Name { get; set; }
public string Email { get; set; }
public string Address { get; set; }
public int? ContactNumber { get; set; }
}
Then change your function to the following:
public List<CustomerMinInfo> GetAllCust()
{
var results = db.Customers.Select(x => new CustomerMinInfo()
{
Name = x.CustName,
Email = x.Email,
Address = x.Address,
ContactNumber = x.CustContactNo
})
.ToList();
return results;
}
This will work, however, you will lose all relationship to the database context. This means if you update the returned values, it will not stick it back into the database.
Also, just to repeat my comment, returning more columns (with the exception of byte arrays) does not necessarily mean longer execution time. Returning a lot of rows means more execution time. Your function is returning every single customer in the database, which when your system grows, will start to hang your program, even with the reduced amount of columns.
You are selecting to an anonymous type, which is not a Customer.
If you want to do (sort of) this, you can write it like this:
return db.Customers.Select(x => new Customer { Name = x.CustName, Email = x.CustEmail, Address = x.CustAddress, ContactNo = x.ContactNo }).ToList();
This assumes the properties on your Customer object are what I called them.
** EDIT ** Per your comment,
If you want to return a subset of the table, you can do one of two things:
Return the translated form of Customer as I specified above, or:
Create a new class for your business layer that only has only those four fields, and change your method to return a List<ShrunkenCustomer> (assuming ShunkenCustomer is the name that you choose for your new class.)
GetAllCust() is supposed to return a List of Customer, Select New will create a list of Anonymous Types, you need to return a list of Customer from your query.
try:
var results = db.Customers.Select( new Customer{CustName = x.CustName}).ToList(); //include other fields
I guess Customer is a class you have defined yourself?
The my suggestion would be to do something like the following:
var results = db.Customers.Select(x => new Customer(x.Custname, x.CustEmail, x.CustAddress, x.CustContactNo)).ToList();
The reason is that you are trying to return a list of Customer but the results from your link is an anonymous class containing those four values.
This would of course require that you have a constructor that takes those four values.
Basically whatever u got in var type, loop on that and store it in list<> object then loop and achieve ur target.Here I m posting code for Master details.
List obj = new List();
var orderlist = (from a in db.Order_Master
join b in db.UserAccounts on a.User_Id equals b.Id into abc
from b in abc.DefaultIfEmpty()
select new
{
Order_Id = a.Order_Id,
User_Name = b.FirstName,
Order_Date = a.Order_Date,
Tot_Qty = a.Tot_Qty,
Tot_Price = a.Tot_Price,
Order_Status = a.Order_Status,
Payment_Mode = a.Payment_Mode,
Address_Id = a.Address_Id
});
List<MasterOrder> ob = new List<MasterOrder>();
foreach (var item in orderlist)
{
MasterOrder clr = new MasterOrder();
clr.Order_Id = item.Order_Id;
clr.User_Name = item.User_Name;
clr.Order_Date = item.Order_Date;
clr.Tot_Qty = item.Tot_Qty;
clr.Tot_Price = item.Tot_Price;
clr.Order_Status = item.Order_Status;
clr.Payment_Mode = item.Payment_Mode;
clr.Address_Id = item.Address_Id;
ob.Add(clr);
}
using(ecom_storeEntities en=new ecom_storeEntities())
{
var Masterlist = en.Order_Master.OrderByDescending(a => a.Order_Id).ToList();
foreach (var i in ob)
{
var Child = en.Order_Child.Where(a => a.Order_Id==i.Order_Id).ToList();
obj.Add(new OrderMasterChild
{
Master = i,
Childs = Child
});
}
}
I am returning a list of restaurants that pulls information from the RESTAURANT, CUISINE, CITY, and STARRATING tables. I want to get a list of each restaurant with its associated city and cuisine along with the average rating in the STARRATING table. This is what I have, so far ... Thanks in advance.
RestaurantsEntities db = new RestaurantsEntities();
public List<RESTAURANT> getRestaurantsWRating(string cuisineName, string cityName, string priceName, string ratingName)
{
var cuisineID = db.CUISINEs.First(s => s.CUISINE_NAME == cuisineName).CUISINE_ID;
List<RESTAURANT> result = (from RESTAURANT in db.RESTAURANTs.Include("CITY").Include("CUISINE").Include("STARRATING")
where RESTAURANT.CUISINE_ID == cuisineID
orderby RESTAURANT.REST_NAME ascending
select RESTAURANT).ToList();
return result;
}
From what you have it looks like Restaurant has a STARRATING collection. If so, this is what you can do:
from r in db.Restaurants
where r.CUISINE_ID == cuisineID
orderby r.REST_NAME ascending
select new {
Restaurant = r,
City = r.CITY,
Cuisine = r.CUISINE,
AvgRating = r.STARRATING.Average(rt => rt.Rating)
}
You'd need to give more informations about your classes and associations (preferably a class diagram) if this is not right.
(BTW using capitals for class and property names is not conventional).
First I would wrap your whole code block above in a using statement:
using(RestaurantEntities db = new RestaurantEntities())
{
...
}
This will help with cleanup for the EF context.
The way I would typically do this is if you have control of your database, I would create a view in the database that does this work, add the view to your entity model and query the view. This simplifies the whole process and offloads the work of the aggregation to the database.
If you don't have control over the database or don't prefer the view technique then I would query using the include technique as you have done and then add a partial class to RESTAURANT (if using model-first) in order to add an AverageRating property and then manually calculate the average for each related STARRATING set of related rows and apply the resultant value to the added property. You could do this through linq to objects once you have all the data back. This technique would not scale very well as more data is accumulated unless you are confident you never return but one or a few RESTAURANT instances. You could use something like:
//query data as you have done above...
foreach(RESTAURANT r in result)
{
if(r.STARRATING.Count() > 0)
{
r.AverageRating = r.STARRATING.Average(rating => rating.Value); //.Value is your field name
}
else
{
r.AverageRating = 0; // or whatever default you prefer...
}
}
Hope this helps.