I have created my model objects (DTO's) from EF's code first approach from an existing database and table selection. I am able to join multiple tables using method syntax but query syntax's fails to initialize object on the second dbcontext while joining.
I tried to replicate if method syntax works and it does work but query syntax doesn't except the first statement and fetching from single table.
Method syntax
var customers = procontext.Customer
.Join(procontext.ROLODEX, cust => cust.rolodex_sak,
rol => rol.rolodex_sak,
(cust, rol) => new { customerid = cust.customer.code, fname = rol.lname)});
Query Syntax
var customers = from cust in procontext.Customer
join rol in procontext.rolodex on cust.rolodex_sak = rol.
When doing rol and ., it doesn't show any property and when I reverse the line rol fetches all the properties but then cust fails to load customer objects. So only first statement works in query syntax.
My bad I was using "=" instead of equals, it works now.
Related
I have 3 tables. Orders, OrderItems and OrderItemServices. Each order can contain multiple OrderItems and each OrderItem can contain multiple OrderItemServices.
I want to get a list of data of all orders from these tables in Linq. I could write a join but how do I make an anonymous data type to in select clasue which can give me Order list in this hierarchy?
If I use navigation properties and then select OrderItemServices in side select clause shown below it would fire individual select query for each OrderItemService which I want to avoid.
from order in Orders
select new
{
ActiveOrders = order,
ActiveOrderItems =order.OrderItems,
ActiveServices = order.OrderItems.Select(o => o.OrderItemServices)
}
Is it possible to group each order with a structure of multiple items inside it and multiple services inside items?
Refer msdn to start on LINQ To SQL
To get data from three tables you can get idea from the following simple example
var data = (from product in context.Products
from department in context.Departments
from category in context.Categories
where product.DeptId == department.DeptId
&& product.CatId == category.CatId
select new
{
product.Code,
product.Name,
department.Name,
category.Name
}).Distinct.ToList();
You have to set up your context to use eager loading:
var context = new MyDataContext();
var options = new DataLoadOptions();
options.LoadWith<Orders>(x => x.OrderItems);
options.LoadWith<OrderItems>(x => x.OrderItemServices);
context.LoadOptions = options;
var query = from order in context.Orders // ... etc
Then sub items will be included in initial query result and won't cause additional requests to the database. This will use JOIN internally to retrieve all the data in one go. You can check generated SQL using SQL Server Profiler.
http://blog.stevensanderson.com/2007/12/02/linq-to-sql-lazy-and-eager-loading-hiccups/
I've found plenty of info on how to select multiple result sets with stored procedures but nothing substantial on how to do so with a linq query.
For example, I can do sub-queries that return mulitple sets of results with something like
var query = (from school in context.Schools
where school.id == someId
select new
{
subSetA = (from student in context.Students
select student).ToList(),
subSetB = (from building in context.Buildings
select building).ToList(),
}).First();
query.subSetA; //Access subSetA
query.subSetB; //Access subSetB
Which works fine, but what if I just want to select both subSetA and subSetB without querying against the school table? I want to select two separate sets of data that gets sent to the server in one query.
Any information as to how to do this with EF 6 would be great.
Well, I'm sure there are many ways to do this, but if you want to avoid introducing a third DbSet into the mix...
var query = (from s in context.Students.Take(1)
select new
{
subSetA = context.Students.ToList(),
subSetB = context.Buildings.ToList(),
})
Then, you can use query.ToList() or maybe using query.Load() and working with context.Students.Local, etc. would work.
I am doing 2 linq queries one with entity framework and the other is linq to sql and they are not playing well together at all.
The first query grabs id's that are in one table via entity framework.
var pemdata = from pd in db.tblMap
where pd.PID == pid
select new
{
eid = pd.EID
};
And then I'm filtering the second query using a contains via linq to sql.
var data = from e in p.entities
join et in p.entity_types on e.entity_type equals et.entity_types_id
where pemdata.Contains(e.entity_id)
select new gEntities
{
entity_type = e.entity_type.ToString(),
Name = e.entity_name,
Type = et.entity_types_name,
Address = e.entity_address,
City = e.entity_city,
Zip = e.entity_zip.ToString()
};
The issue I'm seeing is an error.
Instance argument: cannot convert from 'System.Linq.IQueryable' to
'System.Linq.ParallelQuery'
'System.Linq.IQueryable' does not contain a definition for 'Contains' and the best extension method overload
'System.Linq.ParallelEnumerable.Contains(System.Linq.ParallelQuery,
TSource)' has some invalid arguments
I usually don't have a problem doing a contains like this. but when I'm mixing linq to sql and entity framework I get this issue.
Any thoughts?
You'll need to materialize the first query before using the results. Easiest way is to just call .ToList() on it. Then you can use the results in the second query.
var pemdata = (from pd in db.tblMap
where pd.PID == pid
select pd.EID).ToList();
I would like to query a DataTable that produces a DataTable that requires a subquery. I am having trouble finding an appropriate example.
This is the subquery in SQL that I would like to create:
SELECT *
FROM SectionDataTable
WHERE SectionDataTable.CourseID = (SELECT SectionDataTable.CourseID
FROM SectionDataTable
WHERE SectionDataTable.SectionID = iSectionID)
I have the SectionID, iSectionID and I would like to return all of the records in the Section table that has the CourseID of the iSectionID.
I can do this using 2 separate queries as shown below, but I think a subquery would be better.
string tstrFilter = createEqualFilterExpression("SectionID", strCriteria);
tdtFiltered = TableInfo.Select(tstrFilter).CopyToDataTable();
iSelectedCourseID = tdtFiltered.AsEnumerable().Select(id => id.Field<int>("CourseID")).FirstOrDefault();
tdtFiltered.Clear();
tstrFilter = createEqualFilterExpression("CourseID", iSelectedCourseID.ToString());
tdtFiltered = TableInfo.Select(tstrFilter).CopyToDataTable();
Although it doesn't answer your question directly, what you are trying to do is much better suited for an inner join:
SELECT *
FROM SectionDataTable S1
INNER JOIN SectionDataTable S2 ON S1.CourseID = S2.CourseID
WHERE S2.SectionID = iSectionID
This then could be modeled very similarily using linq:
var query = from s1 in SectionDataTable
join s2 in SectionDataTable
on s1.CourseID equals s2.CourseID
where s2.SectionID == iSectionID
select s1;
When working in LINQ you have to think of the things a bit differently. Though you can go as per the Miky's suggestion. But personally I would prefer to use the Navigational properties.
For example in your given example I can understand that you have at-least 2 tables,
Course Master
Section Master
One Section must contain a Course reference
Which means
One Course can be in multiple Sections
Now if I see these tables as entities in my model I would see navigational properties as,
Course.Sections //<- Sections is actually a collection
Section.Course //<- Course is an object
So the same query can be written as,
var lstSections = context.Sections.Where(s => s.Course.Sections.Any(c => c.SectionID == iSectionID)).ToList();
I think you main goal is, you are trying extract all the Sections where Courses are same as given Section's Courses.
I am using Linq to SQL in Linqpad to get to some data.
I have 3 tables I need to use to do the following steps:
1) Select customers by postcode (Customer table)
2) Get all transaction ID's for these customers (Transaction table)
3) Get itemized items for all transaxction ID's (Itemized table)
So i start out easy enough and grab the customers:
string pc = "123";
var cust =
from c in Customers
where c.PostCode.StartsWith(pc) == true
select c;
Now I need to create a new Linq object that has the lookup from transaction table based on the "CustomerID" field but I am not sure how to do this. Ive experimented with some foreach loops but cant get syntax right. Did some googling and saw posts saying not to use foreach loops with linq objects as you should use inbuilt Linq functionality but I couldnt find any examples doing what I needed.
I apologise for such a basic question but I have just started using Linq.
How do I create the next Linq object with all transaction records based on the CustoomerID field?
You can use single query with joins. If you have navigation properties in your entities:
from c in Customers
from t in c.Transactions
from i in t.ItemizedItems
where c.PostCode.StartsWith(pc)
select i
Labda syntax:
Customers.Where(c => c.PostCode.StartsWith(pc))
.SelectMany(c => c.Transactions)
.SelectMany(t => t.ItemizedItems);
If you don't have navigation properties:
from c in Customers
join t in Transactions on c.ID equals t.CustomerID
join i in t.ItemizedItems on t.ID equals i.TransactionID
where c.PostCode.StartsWith(pc)
select i