Does Hibernate + NhibernateLINQ support projection of inner objects.
for eg. when I try the following I get an Index out of bounds exception on Patient object on the call to Queryable.ToList()
var registrations = from r in _session.Linq<Domain.Registration>().Expand("Patient") select r;
var queryable = registrations.Select(
r => new { r.Id, r.AccountNumber, r.DateAdded, r.DateUpdated, r.Patient.FamilyName, r.Patient});
var list = queryable.ToList();
var workListItems = new List<WorkListItem>();
foreach (var anonymous in list)
{
var w = new WorkListItem
{
Id = anonymous.Id,
ClientAccountId = anonymous.AccountNumber,
DateAdded = anonymous.DateAdded,
DateUpdated = anonymous.DateUpdated,
Patient = anonymous.Patient
};
workListItems.Add(w);
}
return workListItems;
The legacy contrib provider has problems with this kind of query.
The new integrated provider in NHibernate 3 handles them without problems.
As of 2010-09-30, Alpha3 is quite stable (with most efforts directed to improving the Linq provider even more), and a GA release is expected before the end of the year.
Related
I have a system with two database servers I am working with:
One of them is database first - a database managed by a legacy enterprise application and I don't have full control over changing the database structure.
The second is code first and I have full control in the code first database to make changes.
Security policies prevent me from making a view that joins tables from the two database servers in the code first DB which might be a way to make this better according to what i've seen on SO posts.
I have one context for each database since they are separate.
The data and structure in the code first tables is designed to be able to join to the non-code first database as if they were all in one database.
I CAN get what I need working using this set of queries:
// Set up EF tables
var person = await _context1.Person.ToListAsync();
var labor = await _context1.Labor.ToListAsync();
var laborCraftRate = await context1.LaborCraftRate.ToListAsync();
var webUsers = await context2.WebUsers.ToListAsync();
var workOrders = await _context1.Workorder
.Where(r => r.Status == "LAPPR" || r.Status == "APPR" || r.Status == "REC")
.ToListAsync();
var specialRequests = await _context1.SwSpecialRequest
.Where(r => r.Requestdate > DateTime.Now)
.ToListAsync();
var distributionListQuery = (
from l in labor
from p in person.Where(p => p.Personid == l.Laborcode).DefaultIfEmpty()
from wu in webUsers.Where(wu => wu.Laborcode == l.Laborcode).DefaultIfEmpty()
from lcr in laborCraftRate.Where(lcr => lcr.Laborcode == l.Laborcode).DefaultIfEmpty()
select new
{
Laborcode = l.Laborcode,
Displayname = p.Displayname,
Craft = lcr.Craft,
Crew = l.Crewid,
Active = wu.Active,
Admin = wu.FrIsAdmin,
FrDistLocation = wu.FrDistLocation,
}).Where(r => r.Active == "Y" && (r.FrDistLocation == "IPC" || r.FrDistLocation == "IPC2" || r.FrDistLocation == "both"))
.OrderBy(r => r.Craft)
.ThenBy(r => r.Displayname);
// Build a subquery for the next query to use
var ptoSubQuery =
from webUser in webUsers
join workOrder in workOrders on webUser.Laborcode equals workOrder.Wolablnk
join specialRequest in specialRequests on workOrder.Wonum equals specialRequest.Wonum
select new
{
workOrder.Wonum,
Laborcode = workOrder.Wolablnk,
specialRequest.Requestdate
};
// Build the PTO query to join with the distribution list
var ptoQuery =
from a in ptoSubQuery
group a by a.Wonum into g
select new
{
Wonum = g.Key,
StartDate = g.Min(x => x.Requestdate),
EndDate = g.Max(x => x.Requestdate),
Laborcode = g.Min(x => x.Laborcode)
};
// Join the distribution list and the object list to return
// list items with PTO information
var joinedQuery = from dl in distributionListQuery
join fl in ptoQuery on dl.Laborcode equals fl.Laborcode
select new
{
dl.Laborcode,
dl.Displayname,
dl.Craft,
dl.Crew,
dl.Active,
dl.Admin,
dl.FrDistLocation,
fl.StartDate,
fl.EndDate
};
// There are multiple records that result from the join,
// strip out all but the first instance of PTO for all users
var distributionList = joinedQuery.GroupBy(r => r.Laborcode)
.Select(r => r.FirstOrDefault()).OrderByDescending(r => r.Laborcode).ToList();
Again, this works and gets my data back in a reasonable but clearly not optimal timeframe that I can work with in my UI that needs this by preloading the data before it is needed. Not the best, but works.
If I change the variable declarations to not be async which I was told I should do in another SO post, this turns into a cross db query and netcore says no:
// Set up EF tables
var person = _context1.Person;
var labor = _context1.Labor;
var laborCraftRate = context1.LaborCraftRate;
var webUsers = context2.WebUsers;
var workOrders = _context1.Workorder
.Where(r => r.Status == "LAPPR" || r.Status == "APPR" || r.Status == "REC");
var specialRequests = _context1.SwSpecialRequest
.Where(r => r.Requestdate > DateTime.Now);
Adding ToListAsync() is what allows the join functionality I need to work.
Q - Can anyone elaborate on possible downsides and problems with what I am doing?
Thank you for helping me understand!
It's not that calling ToList() "doesn't work." The problem is that it materializes (I think that's the right word) the query and returns a potentially larger than intended amount of data to the client. Any further LINQ operations are done on the client side. This can increase the load on the database and network. In your case, it works because you're bringing all that data to the client side. At that point, it no longer matters that it was a cross-database query.
This was a frequent concern during the transition from .NET Core 2.x to 3.x. If an operation could not be performed server side, .NET Core 2.x would silently insert something like ToList(). (Well, not completely silently. I think it was logged somewhere. But many developers weren't aware of it.) 3.x stopped doing that and would give you an error. When people tried to upgrade to 3.x, they often found it difficult to convert the queries into something that could run server side. And people resisted throwing in an explicit ToList() because muh performance. But remember, that's what it was always doing. If there wasn't a performance issue before, there isn't one now. And at least now you're aware of what it's actually doing, and can fix it if you really need to.
_context.Update(v) ;
_context.SaveChanges();
When I use this code then SQL Server adds a new record instead of updating the
current context
[HttpPost]
public IActionResult PageVote(List<string> Sar)
{
string name_voter = ViewBag.getValue = TempData["Namevalue"];
int count = 0;
foreach (var item in Sar)
{
count = count + 1;
}
if (count == 6)
{
Vote v = new Vote()
{
VoteSarparast1 = Sar[0],
VoteSarparast2 = Sar[1],
VoteSarparast3 = Sar[2],
VoteSarparast4 = Sar[3],
VoteSarparast5 = Sar[4],
VoteSarparast6 = Sar[5],
};
var voter = _context.Votes.FirstOrDefault(u => u.Voter == name_voter && u.IsVoted == true);
if (voter == null)
{
v.IsVoted = true;
v.Voter = name_voter;
_context.Add(v);
_context.SaveChanges();
ViewBag.Greeting = "رای شما با موفقیت ثبت شد";
return RedirectToAction(nameof(end));
}
v.IsVoted = true;
v.Voter = name_voter;
_context.Update(v);
_context.SaveChanges();
return RedirectToAction(nameof(end));
}
else
{
return View(_context.Applicants.ToList());
}
}
You need to tell the DbContext about your entity. If you do var vote = new Vote() vote has no Id. The DbContext see this and thinks you want to Add a new entity, so it simply does that. The DbContext tracks all the entities that you load from it, but since this is just a new instance, it has no idea about it.
To actually perform an update, you have two options:
1 - Load the Vote from the database in some way; If you get an Id, use that to find it.
// Loads the current vote by its id (or whatever other field..)
var existingVote = context.Votes.Single(p => p.Id == id_from_param);
// Perform the changes you want..
existingVote.SomeField = "NewValue";
// Then call save normally.
context.SaveChanges();
2 - Or if you don't want to load it from Db, you have to manually tell the DbContext what to do:
// create a new "vote"...
var vote = new Vote
{
// Since it's an update, you must have the Id somehow.. so you must set it manually
Id = id_from_param,
// do the changes you want. Be careful, because this can cause data loss!
SomeField = "NewValue"
};
// This is you telling the DbContext: Hey, I control this entity.
// I know it exists in the DB and it's modified
context.Entry(vote).State = EntityState.Modified;
// Then call save normally.
context.SaveChanges();
Either of those two approaches should fix your issue, but I suggest you read a little bit more about how Entity Framework works. This is crucial for the success (and performance) of your apps. Especially option 2 above can cause many many issues. There's a reason why the DbContext keep track of entities, so you don't have to. It's very complicated and things can go south fast.
Some links for you:
ChangeTracker in Entity Framework Core
Working with Disconnected Entity Graph in Entity Framework Core
I'm currently using Entity Framework for my db access but want to have a look at Dapper. I have classes like this:
public class Course{
public string Title{get;set;}
public IList<Location> Locations {get;set;}
...
}
public class Location{
public string Name {get;set;}
...
}
So one course can be taught at several locations. Entity Framework does the mapping for me so my Course object is populated with a list of locations. How would I go about this with Dapper, is it even possible or do I have to do it in several query steps?
Alternatively, you can use one query with a lookup:
var lookup = new Dictionary<int, Course>();
conn.Query<Course, Location, Course>(#"
SELECT c.*, l.*
FROM Course c
INNER JOIN Location l ON c.LocationId = l.Id
", (c, l) => {
Course course;
if (!lookup.TryGetValue(c.Id, out course))
lookup.Add(c.Id, course = c);
if (course.Locations == null)
course.Locations = new List<Location>();
course.Locations.Add(l); /* Add locations to course */
return course;
}).AsQueryable();
var resultList = lookup.Values;
See here https://www.tritac.com/blog/dappernet-by-example/
Dapper is not a full blown ORM it does not handle magic generation of queries and such.
For your particular example the following would probably work:
Grab the courses:
var courses = cnn.Query<Course>("select * from Courses where Category = 1 Order by CreationDate");
Grab the relevant mapping:
var mappings = cnn.Query<CourseLocation>(
"select * from CourseLocations where CourseId in #Ids",
new {Ids = courses.Select(c => c.Id).Distinct()});
Grab the relevant locations
var locations = cnn.Query<Location>(
"select * from Locations where Id in #Ids",
new {Ids = mappings.Select(m => m.LocationId).Distinct()}
);
Map it all up
Leaving this to the reader, you create a few maps and iterate through your courses populating with the locations.
Caveat the in trick will work if you have less than 2100 lookups (Sql Server), if you have more you probably want to amend the query to select * from CourseLocations where CourseId in (select Id from Courses ... ) if that is the case you may as well yank all the results in one go using QueryMultiple
No need for lookup Dictionary
var coursesWithLocations =
conn.Query<Course, Location, Course>(#"
SELECT c.*, l.*
FROM Course c
INNER JOIN Location l ON c.LocationId = l.Id
", (course, location) => {
course.Locations = course.Locations ?? new List<Location>();
course.Locations.Add(location);
return course;
}).AsQueryable();
I know I'm really late to this, but there is another option. You can use QueryMultiple here. Something like this:
var results = cnn.QueryMultiple(#"
SELECT *
FROM Courses
WHERE Category = 1
ORDER BY CreationDate
;
SELECT A.*
,B.CourseId
FROM Locations A
INNER JOIN CourseLocations B
ON A.LocationId = B.LocationId
INNER JOIN Course C
ON B.CourseId = B.CourseId
AND C.Category = 1
");
var courses = results.Read<Course>();
var locations = results.Read<Location>(); //(Location will have that extra CourseId on it for the next part)
foreach (var course in courses) {
course.Locations = locations.Where(a => a.CourseId == course.CourseId).ToList();
}
Sorry to be late to the party (like always). For me, it's easier to use a Dictionary, like Jeroen K did, in terms of performance and readability. Also, to avoid header multiplication across locations, I use Distinct() to remove potential dups:
string query = #"SELECT c.*, l.*
FROM Course c
INNER JOIN Location l ON c.LocationId = l.Id";
using (SqlConnection conn = DB.getConnection())
{
conn.Open();
var courseDictionary = new Dictionary<Guid, Course>();
var list = conn.Query<Course, Location, Course>(
query,
(course, location) =>
{
if (!courseDictionary.TryGetValue(course.Id, out Course courseEntry))
{
courseEntry = course;
courseEntry.Locations = courseEntry.Locations ?? new List<Location>();
courseDictionary.Add(courseEntry.Id, courseEntry);
}
courseEntry.Locations.Add(location);
return courseEntry;
},
splitOn: "Id")
.Distinct()
.ToList();
return list;
}
Something is missing. If you do not specify each field from Locations in the SQL query, the object Location cannot be filled. Take a look:
var lookup = new Dictionary<int, Course>()
conn.Query<Course, Location, Course>(#"
SELECT c.*, l.Name, l.otherField, l.secondField
FROM Course c
INNER JOIN Location l ON c.LocationId = l.Id
", (c, l) => {
Course course;
if (!lookup.TryGetValue(c.Id, out course)) {
lookup.Add(c.Id, course = c);
}
if (course.Locations == null)
course.Locations = new List<Location>();
course.Locations.Add(a);
return course;
},
).AsQueryable();
var resultList = lookup.Values;
Using l.* in the query, I had the list of locations but without data.
Not sure if anybody needs it, but I have dynamic version of it without Model for quick & flexible coding.
var lookup = new Dictionary<int, dynamic>();
conn.Query<dynamic, dynamic, dynamic>(#"
SELECT A.*, B.*
FROM Client A
INNER JOIN Instance B ON A.ClientID = B.ClientID
", (A, B) => {
// If dict has no key, allocate new obj
// with another level of array
if (!lookup.ContainsKey(A.ClientID)) {
lookup[A.ClientID] = new {
ClientID = A.ClientID,
ClientName = A.Name,
Instances = new List<dynamic>()
};
}
// Add each instance
lookup[A.ClientID].Instances.Add(new {
InstanceName = B.Name,
BaseURL = B.BaseURL,
WebAppPath = B.WebAppPath
});
return lookup[A.ClientID];
}, splitOn: "ClientID,InstanceID").AsQueryable();
var resultList = lookup.Values;
return resultList;
There is another approach using the JSON result. Even though the accepted answer and others are well explained, I just thought about an another approach to get the result.
Create a stored procedure or a select qry to return the result in json format. then Deserialize the the result object to required class format. please go through the sample code.
using (var db = connection.OpenConnection())
{
var results = await db.QueryAsync("your_sp_name",..);
var result = results.FirstOrDefault();
string Json = result?.your_result_json_row;
if (!string.IsNullOrEmpty(Json))
{
List<Course> Courses= JsonConvert.DeserializeObject<List<Course>>(Json);
}
//map to your custom class and dto then return the result
}
This is an another thought process. Please review the same.
I have a scenario where I have to update an entity if it exists or add a new one if it doesn't.
I would like to execute a single method for this (it would be great if it were a single trip to the server).
Is there something like that in EF?
Right now my code looks like this:
var entity = db.Entities.FirstOrDefault(e => e.Id == myId);
if (entity == null)
{
entity = db.Entities.CreateObject();
entity.Id = myId;
}
entity.Value = "my modified value";
db.SaveChanges();
But I would like to avoid the first query, something like this:
var entity = new Entity();
entity.Id = myId;
entity.Value = "my modified value";
db.AddOrAttach(entity);
db.SaveChanges();
Is there anything similar? or do I have to perform the first query no matter what?
Thanks
You have to perform the first query no matter what, unfortunately.
One option would be to write a stored procedure that performs a T-SQL MERGE then map it to a function import, though that would require that you pass the scalar values of the entity as parameters (and support for navigation properties would be done), but it would accomplish what you're after.
I ran some quick test code for editing in MVC 3 with EF 4 and it seems to work for edit with following code:
using (var context = new TestStackOverFlowEntities())
{
Person p = new Person();
p.Id = long.Parse(collection["Id"]);
p.FirstName = collection["FirstName"];
p.LastName = collection["LastName"];
context.People.Attach(p);
context.ObjectStateManager.ChangeObjectState(p, System.Data.EntityState.Modified);
context.SaveChanges();
return RedirectToAction("Index");
}
Edit: I checked with creating new object too, you need to change this
context.ObjectStateManager.ChangeObjectState(p, System.Data.EntityState.Added);
when Id == 0 //ie new object.
Quick and dirty code to add new is this:
using (var context = new TestStackOverFlowEntities())
{
Person p = new Person();
p.Id = 0;
p.FirstName = collection["FirstName"];
p.LastName = collection["LastName"];
context.People.Attach(p);
context.ObjectStateManager.ChangeObjectState(p, System.Data.EntityState.Added);
context.SaveChanges();
return RedirectToAction("Index");
}
If you are just trying to limit code to clarify your controllers:
db.Attach(model);
db.SaveChanges(model);
Will update if the Entity Key exists, and create if it does not.
I am new to NHibernate and I want to have a count of rows from database. Below is my code,
SearchTemplate template = new SearchTemplate();
template.Criteria = DetachedCriteria.For(typeof(hotel));
template.Criteria.Add(Restrictions.Lt("CheckOutDate", SelDate) || Restrictions.Eq("CheckOutDate", SelDate));
template.Criteria.Add(Restrictions.Eq("Canceled", "False"));
int count = template.Criteria.SetProjection(Projections.Count("ID"));
It gives me an error when I try to compile app that says
"Cannot implicitly convert type 'NHibernate.Criterion.DetachedCriteria' to 'int'"
I want to have a count of rows of the table hotel..
You want to use GetExecutableCriteria:
SearchTemplate template = new SearchTemplate();
template.Criteria = DetachedCriteria.For(typeof(hotel));
template.Criteria.Add(Restrictions.Lt("CheckOutDate", SelDate) || Restrictions.Eq("CheckOutDate", SelDate));
template.Criteria.Add(Restrictions.Eq("Canceled", "False"));
var count = DoCount(template.Criteria, session /* your session */);
public long DoCount(DetachedCriteria criteria, ISession session)
{
return Convert.ToInt64(criteria.GetExecutableCriteria(session)
.SetProjection(Projections.RowCountInt64())
.UniqueResult());
}
On a side note, you should take a look at using NHibernate.Linq:
var result = (from h in Session.Linq<Hotel>()
where h.CheckOutDate <= SelDate
where h.Canceled != true
select h).Count();
More information here.