I have an application where I have a model composed of several other objects. For instance:
class Customer
{
public int CustomerId{get;set;}
public int? AddressId {get;set;} // this is set as allow null in database
public string Name {get;set}
public virtual Addresss Address {get;set;}
}
class Address
{
public int AddressId {get;set}
public string A1 {get;set}
}
The idea is to use context.customers.include("Address"). However the model I am currently working on is much more complex than the above.
I have used https://stackoverflow.com/a/51772067 as a reference, but unfortunately this does not work for an id having no value (nullable, as the database allows nulls)
How can I modified the expression to behave as a true left join (includes an empty entity if the id is null).
Thanks in advance for your assistance
As per the official doc you could do left join as below
List<Person> people = new List<Person> { magnus, terry, charlotte, arlene };
List<Pet> pets = new List<Pet> { barley, boots, whiskers, bluemoon, daisy };
var query = from person in people
join pet in pets on person equals pet.Owner into gj
from subpet in gj.DefaultIfEmpty()
select new { person.FirstName, PetName = subpet?.Name ?? String.Empty };
When you use DefaultIfEmpty() then it becomes a left join.
Upvote if it works.
Related
I have a model -
public class EmployeeModel
{
public int Id { get; set; }
public string Name { get; set; }
public string Designation { get; set; }
public double? Salary { get; set; }
}
and a LINQ method syntax like -
public List<EmployeeModel> GetEmployees()
{
using (var DbCon = new OfficeEntities())
{
var result = DbCon.Employee.Select(x => new EmployeeModel()
{
Id = x.Id,
Name = x.Name
//Salary = x.Salary,
//Designation = x.Designation
})
.ToList();
return result;
}
}
I have commented out salary and designation but even though it prints with
key : salary and for value i:null="true" why
result comes like this
<EmployeeModel>
<Designation i:nil="true"/>
<Id>1</Id>
<Name>Sulochana </Name>
<Salary i:nil="true"/>
</EmployeeModel>
Even though commented/removed the parameters in the query, why it is appearing in the result. Kindly help
Because you didn't include those properties in the projection.
This has a special meaning for the client to interpret, it's not that these fields have a null value, these fields we're not included in the projection, so their values are indeterminate.
If the client has requesting a projection with $select=Id,Name then these fields would not have been included at all, but because the client is expecting all the fields this is how the API expresses to the client that the fields we're deliberately omitted, but to satisfy the return contract the fields must be provided in some form.
This answer is assuming OP is writing an OData service, but the same concept applies with Linq to Entities in general. If the Linq expression is projecting into a model type, but not including certain fields, then those fields will have an uninitialized value on the model instances that are projected out.
You are creating an EmployeeModel object in the Select projection. Hence, Salary and Designation are being initialized with their default values, even though you didn't set values for them. Then after serializing all properties are present in the result.
If you are expecting only Id and Name in the output/result, then define a type in that shape -
public class EmployeeInfo
{
public int Id { get; set; }
public string Name { get; set; }
}
and create an object of that type in the projection -
var result = DbCon.Employee.Select(x => new EmployeeInfo()
{
Id = x.Id,
Name = x.Name
})
.ToList();
I have the following classes:
public class Customer {
public int Id {get;set;}
public string Name {get;set;}
public List<Order> Orders {get;set;}
//other attributes
}
public class Order{
public int Id {get;set;}
public string Name {get;set;}
public decimal Value {get;set;}
}
Given a customerId I wish to only select the customer name and the order Id using projection in EF.
I am doing the following:
IQueryable<Customer> customer = DataContextFactory.GetDataContext().Set<Customer>();
var tempCustomer = customer.Where(x => x.Id == customerId).Select( c=>
new
{
Name = c.Name
}
)
This gives me the customer name. Which I can then pass back to the entity like so:
var customerToReturn = tempCustomer.ToList().Select(x => new Customer
{ Name = x.Name});
If I include the order on the query like this:
var tempCustomer = customer.Where(x => x.Id == customerId).Select( c=>
new
{
Name = c.Name,
Orders = new {
Id = c.Orders.Id
}
}
)
Then I get a duplicate customer per order line (as per the SQL generated by EF). Is there a way I can inline this generation into a single SQL call?
Currently I am getting around this by calling each child object separately.
I'm trying to find out how I would define the code first navigation properties on these two classes to perform something similiar to this query:
SELECT USERID, FIRSTNAME, LASTNAME, COURSEID, NAME
FROM User
LEFT OUTER JOIN Course ON User.USERID = Course.USERID
WHERE COURSEID = 1
So I'm trying to find a list of users together with if they have attended a certain course.
public class User
{
public int UserId {get;set; }
public string FirstName {get;set;}
public string LastName {get;set;}
public virtual ICollection<Course> Courses { get; set; }
}
public class Course
{
public int CourseId { get;set; }
public int UserId { get;set; }
public string Name { get;set; }
public virtual User User {get;set;}
}
If I was to write a query to achieve this
var u = Users.Where(x => x.Courses.Any(x => x.CourseId = 1));
This does a subquery, which is not what I wanted (as people who didnt attend the course would not show).
How would the navigation property be defined?
HasMany(t => t.Courses).WithOptional(t => t.User).HasForeignKey(t => t.UserId);
Check this link:
http://msdn.microsoft.com/en-us/library/vstudio/bb397895.aspx
Left outer joins in LINQ are done via DefaultIfEmpty method.
var u = Users.Select ( x => new {
User = x,
AttendedCourse = x.Courses.Any()
} );
For specific course id,
var u = Users.Select ( x => new {
User = x,
AttendedCourse = x.Courses.Any( c => c.CourseID == 1 )
} );
Sub query is the only way to write related queries, However, EF will choose the best suitable join type and will give you correct results. And EF can manage mostly all kinds of queries without doing joins.
Got a very difficult EntityFramework Code First question. I'll keep this as simple as possible.
Imagine we have n number of classes, lets start with 2 for now
public class Person
{
public string Name { get; set; }
}
public class Address
{
public string AddressLine1 { get; set; }
public string AddressLine2 { get; set; }
}
Now then, what I want to do is be able to search the domain model with a single string, i.e. something like DbContext.Search( "Foo" ). The call would search both the person and address tables for a string match and would return a list populated with both Person and Address entities.
Have to say I am not entirely clear how to go about it but I am considering using DataAnnotations to do something like this
public class Person
{
**[Searchable]**
public string Name { get; set; }
}
public class Address
{
**[Searchable]**
public string AddressLine1 { get; set; }
**[Searchable]**
public string AddressLine2 { get; set; }
}
Am I on the right track?
Should I use the Fluent API instead?
Reflection?
Any and all thoughts massively appreciated.
the Find method searches only in the Primary Key column. If we don't make any column explicitly primary key column then find method will throw error. Generally EF convention takes propertyName+id as the primary key in the class. But if you want to search with Name then Make add [Key] to the property. it will become primary key and u will be able to find properties.
dbContext.Addresses.find("Foo");
Create a new object type onto which you'll project 2 types of search results:
public class Result
{
public string MainField { get; set; }
// you may have other properties in here.
}
Then find entities of each type that match your criteria, projecting them onto this type:
var personResults = DbContext.Persons
.Where(p => p.Name == "Foo")
.Select(p => new Result{MainField = p.Name});
// don't forget to map to any other properties you have in Result as well
var addressResults = DbContext.Adresses
.Where(a =>
a.AddressLine1 == "Foo" ||
a.AddressLine2 == "Foo"
).
.Select(a => new Result{MainField = a.AddressLine1 + ", " + a.AddressLine2 });
// again, don't forget to map to any other properties in Result
Then merge the lists:
var allResults = personResults.Union(addressResults).ToList();
...at which point you can sort the list however you like.
"Result" and "MainField", are rather generic; just using them because I am not thoroughly aware of your domain model.
I'm trying to create search functionality across a couple of tables, following the pattern in Creating dynamic queries with entity framework
I have 3 tables:
People:
pk ID
varchar FirstName
varchar LastName
fk AddressMap_ID
AddressMap:
pk ID
Address:
pk ID
varchar StreetName
varchar StreeNumber
fk AddressMap_ID
Multiple people can live at one address. I pass in a Search model, and populate the results property:
public class Search
{
public string streetname { get; set; }
public string streetnumber { get; set; }
public string fname { get; set; }
public string lname { get; set; }
public IEnumerable<Results> results { get; set; }
}
public class Results
{
public int AddressID { get; set; }
public string StreetNumber { get; set; }
public string StreetName { get; set; }
public IEnumerable<PeopleResults> people { get; set; }
}
public class PeopleResults
{
public int personID { get; set; }
public string First { get; set; }
public string Last { get; set; }
}
This works if I filter on an address, or name + address:
public void GetResults(Search model)
{
Entities _context;
_context = new Entities();
var addr = from a in _context.Addresses
select a;
addr = addr.Where(filter => filter.StreetNumber == model.streetnumber);
addr = addr.Where(filter => filter.StreetName == model.streetname);
addr = from a in addr
group a by a.AddressMap_ID into addrs
select addrs.FirstOrDefault();
var ppl = from p in addr.SelectMany(p => p.AddressMap.People) select p;
ppl = ppl.Where(filter => filter.FirstName.StartsWith(model.fname));
ppl = ppl.Where(filter => filter.LastName.StartsWith(model.lname));
model.results = from a in addr
select new Results
{
AddressID = a.ID,
StreetName = a.StreetName,
StreetNumber = a.StreetNumber,
people = from p in ppl
select new PeopleResults
{
First = p.FirstName,
Last = p.LastName
}
};
}
But if I just try to filter on a name, it returns a cartesian join - every single address with all of the people that matched.
There are 3 ways to search: filtering on address only, filter on address + name, or filter on name only.
So if someone search for "123 Main", the results should be
123 Main St SticksVille Joe Smith
Jane Smith
Mary Smith
123 Main St Bedrock Fred Flintstone
Wilma Flintstone
A search for "J Smith 123 Main" should return just:
123 Main St SticksVille Joe Smith
Jane Smith
And a search for just "J Smith" should return:
123 Main St SticksVille Joe Smith
Jane Smith
456 Another St Sometown Jerry Smith
Your query looks "symmetric" to me with respect to people and addresses, it only gets "asymmetric" in the final projected result. So, my idea is to express this symmetry in the query as far as possible:
Get a set (IQueryable<Address>, not executed at once) of addresses filtered by street name and street number
Get a set (IQueryable<Person>, not executed at once) of people filtered by the beginning of first name and last name
Join the two sets by AddressMap_ID. The resulting set of people and addresses contains only those pairs that fulfill the filter criteria for addresses and people. If one of the filter criteria for person or address is not supplied (the first and the third of your examples at the bottom of the question) the join happens on the unfiltered set of all people/addresses, i.e. the joined pairs contain always all people of the filtered address (or all addresses of the filtered people)
Group the joined pairs of people and addresses by Address.ID
Project the groups into your Results collection. The group key is the AddressID. StreetName and StreetNumber can be fetched from the first address in each group and the people are projected from the people in each group.
Execute the query
The following code doesn't cover the case specifically that none of the four filter criteria is supplied. It works in that case but would just load all addresses with all people of those addresses. Maybe you want to throw an exception in that case. Or return nothing (model.Results = null or so), then just jump out of the method.
public void GetResults(Search model)
{
using (var _context = new Entities())
{
// "All" addresses
IQueryable<Address> addresses = _context.Addresses;
// "All" people
IQueryable<Person> people = _context.People;
// Build a Queryable with filtered Addresses
if (!string.IsNullOrEmpty(model.streetname))
addresses = addresses.Where(a => a.StreetName
.StartsWith(model.streetname));
if (!string.IsNullOrEmpty(model.streetnumber))
addresses = addresses.Where(a => a.StreetNumber
.StartsWith(model.streetnumber));
// Build a Queryable with filtered People
if (!string.IsNullOrEmpty(model.fname))
people = people.Where(p => p.FirstName == model.fname);
if (!string.IsNullOrEmpty(model.lname))
people = people.Where(p => p.LastName == model.lname);
// Join the two Queryables with AddressMap_ID
// and build group by Address.ID containing pairs of address and person
// and project the groups into the Results collection
var resultQuery = from a in addresses
join p in people
on a.AddressMap_ID equals p.AddressMap_ID
group new { a, p } by a.ID into g
select new Results
{
AddressID = g.Key,
StreetName = g.Select(ap => ap.a.StreetName)
.FirstOrDefault(),
StreetNumber = g.Select(ap => ap.a.StreetNumber)
.FirstOrDefault(),
people = g.Select(ap => new PeopleResults
{
First = ap.p.FirstName,
Last = ap.p.LastName
})
};
// Execute query (the whole code performs one single query)
model.results = resultQuery.ToList();
}
}
I am unsure if I interpret the AddressMap table correctly as a kind of join table for a many-to-many relationship (Address can have many people, Person can have many addresses), but the code above yields the three results of the three queries in your example as expected if the tables are filled like so:
The AddressMap table isn't actually used in the query because Addresses and People table are joined directly via the AddressMap_ID columns.
It seems like an approach like this would probably work:
IQueryable<Person> ppl = _context.People;
ppl = addr.Where(filter=>filter.First.StartsWith(model.fname));
ppl = addr.Where(filter=>filter.Last.StartsWith(model.lname));
var pplIds = ppl.Select(p => p.PersonId);
model.results = from a in addr
where a.AddressMap.People.Any(p => pplIds.Contains(p.PersonId))
select new Results {
AddressID = a.ID,
StreetName = a.StreetName,
StreetNumber = a.StreetNumber,
people = from p in a.People
select new PeopleResults {
First = p.FirstName,
Last = p.LastName
}
};
Rather than basing the people property on the matching people, you want to base the entire address set on the matching people.