I am new at Entity framework, and curious what the best way would be to update all tables with records of new data. I have a method which returns a list of objects with updated records. Most of the information stays the same; just two fields will be updated.
Currently I created two ways of doing that update.
The first one is to get data from the database table and iterate from both Lists to find a match and update that match:
var previousDatafromTable= db.Widgets.ToList();
var newDataReturnedFromMethod =.......
foreach (var d in previousDatafromTable)
{
foreach (var l in newDataReturnedFromMethod )
{
if (d.id == l.id)
{
d.PositionColumn = l.PositionColumn;
d.PositionRow = l.PositionRow;
}
}
The second one is:
foreach (var item in newDataReturnedFromMethod )
{
var model = db.Widgets.Find(item.id);
model.PositionColumn = item.PositionColumn;
model.PositionRow = item.PositionRow;
}
I am iterating through the updated data and updating my database table by ID.
So I am interested to know which method is the better way of doing this, and maybe there is an option in Entity Framework to measure the performance of these two tasks? Thanks for your time in answering.
Neither is really efficient.
The first option loops through newDataReturnedFromMethod for each iteration of previousDatafromTable. That's a lot of iterations.
The second options probably executes a database query for each iteration of newDataReturnedFromMethod.
It's far more efficient to join:
var query = from n in newDataReturnedFromMethod
join p in previousDatafromTable on n.id equals p.id
select new { n,p };
foreach (var pair in query)
{
pair.p.PositionColumn = pair.n.PositionColumn;
pair.p.PositionRow = pair.n.PositionRow;
}
EF doesn't have built-in performance measurements. You'd typically use a profiler for that, or the StopWatch class.
Related
I am using Entity Framework for querying data and I need to merge data already in memory (including new record) with the ones in db.
For example:
var linqdb = from d in context.Set<DEPARTMENT>()
join i in context.Set<INSTALLATION>()
on d.INSTID equals i.INSTID
select new { d.DEPTNAME, i.INSTNAME };
var linqm = from d in context.Set<DEPARTMENT>().Local
join i in context.Set<INSTALLATION>().Local
on d.INSTID equals i.INSTID
select new { d.DEPTNAME, i.INSTNAME };
var linqunion = linqm.Union(linqdb.AsEnumerable());
The difference is only the source where to execute the query:
the first is database the second is in memory.
How I could achieve a result without having to rewrite the LINQ query 2 times?
Regards
Luigi
I am lambda querying models (I make projection with other classes-GameBankVM, GameCouponBankVM) and at the end, I would like to loop throuh query result and update the model field. But I am getting The entity or complex type 'EPINMiddleWareAPI.Models.GameBankVM' cannot be constructed in a LINQ to Entities query.
Here is my sample code:
var gameBankResult = await (context.GameBanks.Where(g => g.productCode == initiate.productCode)
.Take(initiate.quantity)
.Select(g => new GameBankVM
{
quantity = g.quantity,
currency = g.currency,
initiationResultCode = g.initiationResultCode,
productCode = g.productCode,
productDescription = g.productDescription,
referenceId = g.referenceId,
responseDateTime = g.responseDateTime,
unitPrice = g.unitPrice,
totalPrice = g.totalPrice,
coupons = g.coupons.Select(c => new GameCouponBankVM
{
Pin = c.Pin,
Serial = c.Serial,
expiryDate = c.expiryDate
}).ToList()
})).ToListAsync();
if (gameBankResult.Count() != 0)
{
foreach (var item in gameBankResult)
{
item.referenceId = initiate.referenceId;
context.Entry(item).State = System.Data.Entity.EntityState.Modified;
}
await context.SaveChangesAsync();
return Ok(gameBankResult);
}
How can I update referenceId on my GameBank model/table?
In this scenario, your data won't be updated because your query is returning a List of GameBankVM and not a List of GameBank, now technically speaking, you are breaking SRP, you should either update your data or query your data not both in the same method, you may want to refactor your method like this :
1.- Create a private method for data update, in this case, you query directly GameBank iterate thru list entries, make your changes and save them to the database, this same method can return List of GameBank to avoid another database roundtrip.
2.- In the controller after you call your new method, you can run the transformation query to convert List of GameBank to List of GameBankVM and return it to the view.
There are many other ways to do this, I'm just recommending this as a less impact way to make your controller work. But if you are willing to make things better, you can create a business layer where you resolve all your business rules, or you can use patterns like CQS or CQRS.
I am using entity framework 5 for a query like this:
var query =
from i in context.Instrument
from p in i.InstrumentPerformance // 1 : n
where p.PortfolioScenarioID == 6013
select i;
I want to store a queryable respresentation of this (filtered) query in memory. Ideally, I would be able to disconnect the context and still request a specific InstrumentPerformance collection like so:
var perf = query.First(i => i.InstrumentID == 407240).InstrumentPerformance;
But this - of course - does not produce the desired result, since the "perf" object will contain an InstrumentPerformance collection that contains every 1:n joined InstrumentPerformance entity (whether its PortfolioScenarioID is 6013 or not) and it will retrieve these entities via lazy loading, with context.ContextOptions.LazyLoadingEnabled = false (or the context runnning out of scope) the query will not yield anyting.
So this is far from where I want to get: an easy to query in-memory representation from the original query. I tried to materialize into dictionaries and similar approaches, but ended up coding custom data objects for the result which I would like to avoid.
So my question is: what is the recommended method to get such in-memory view?
EDIT:
I am currently using two dictionaries to cache the data, e.g:
var instruments = (
from i in context.Instrument
from p in i.InstrumentPerformance
where p.PortfolioScenarioID == 6013
select i)
.ToDictionary (i => p.InstrumentID, i => i);
var performances = (
from i in context.Instrument
from p in i.InstrumentPerformance
where p.PortfolioScenarioID == 6013
select p)
.ToDictionary (p => p.InstrumentID, p => p);
However, this requires two roundtrips to the database where one seems sufficient and more importantly the semantics for querying the performance data (which is now performances[InstrumentID]) is inconsistent with the EF way of querying (which should be instrument.InstrumentPerformance.First() and the like).
It is possible to retrieve the objects in one take first and then create the dictionaries by:
var query =
(from i in context.Instrument
select new {
i,
ps = i.InstrumentPerformance
.Where(p.PortfolioScenarioID == 6013)
}).AsEnumerable()
.Select(x => x.i);
This materializes and selects Instrument entities and, here's the trick, their partly loaded InstrumentPerformance collections. I.e. the instruments only contain InstrumentPerformance entities that meet the condition PortfolioScenarioID == 6013. This is because EF runs a process known as relationship fixup that ties child objects to the right parent object when they are fetched from the database.
So now you can dispose the context and any time after that do
var perf = query.First(i => i.InstrumentID == 407240).InstrumentPerformance;
or build your dictionaries using from i in query in stead of from i in context.Instrument.
IMPORTANT: lazy loading should be disabled, otherwise EF will still try to load the full collections when they are addressed.
Look at EntityCollection<T> CreateSourceQuery and Attach. I think you could do this (not tested):
var instrumentQuery =
from i in context.Instrument
from p in i.InstrumentPerformance // 1 : n
where p.PortfolioScenarioID == 6013
select i;
var instruments = instrumentQuery.ToList();
foreach (var instrument in instruments) {
var performanceQuery =
instrument.InstrumentPerformance.CreateSourceQuery()
.Where(p => p.PortfolioScenarioID == 6013);
instrument.InstrumentPerformance.Attach(performanceQuery);
}
This executes everything at once (no lazy loading) and has a bit of code duplication, but it would result in a list of Instrument where each i.InstrumentPerformance returns the filtered collection, meaning any subsequent code that operates on it can treat it like any other EF collection without needing to know the details of the query.
This is my real world example.
I have 4 tables:
Person
Plan
Coverage
CoveredMembers
Each person can have many plans, each of those plans can have many coverages. Each of those coverages can have many CoveredMembers.
I need a query that will apply a filter on Plan.PlanType == 1 and CoveredMembers.TermDate == null.
This query should bring back any person who has a medical type plan that is not terminated.
This SQL statement would do just that:
SELECT Person.*, Plans.*, Coverages.*, CoveredMembers.*
FROM Person P
INNER JOIN Plan PL ON P.PersonID = PL.PersonID
INNER JOIN Coverage C on PL.PlanID = C.PlanID
INNER JOIN CoveredMember CM on C.CoverageID = CM.CoverageID
WHERE CM.TermDate = NULL AND PL.PlanType = 1
I have figured out how to do this using anonymous types, but I sometimes need to update the data and save back to the database - and anonymous types are read only.
I was given a solution that did work using JOIN but it only brought back the persons (albeit filtered the way I needed). I can then loop through each person:
foreach (var person in persons) {
foreach (var plan in person.Plans{
//do stuff
}
}
But wouldn't that make a db call for each iteration of the loop? I have 500 persons with 3 unterminated medical plans each, so it would call the db 1500 times?
This is why I want to bring the whole data tree from Persons to CoveredMembers back in one shot. Is this not possible?
I believe this is accomplished in two parts:
Your query to determine the people you wish to have returned based on your criteria as discussed in this question previously: Entity framework. Need help filtering results
Properly setting the navigation properties for entities you want brought together to be eagerly loaded: http://msdn.microsoft.com/en-us/data/jj574232.aspx
For example if your Person entity looks like:
public class Person {
public List<Plan> Plans {get; set;}
...
}
When returning data from the dbcontext you can also use explicit eager loading with the include option:
var people = context.People
.Include(p => p.Plans)
.ToList();
....
If these are nested - coverage is part of plan, etc (which it looks like, it goes something like):
var people = context.People
.Include(p => p.Plans.Select(pl=>pl.Coverage).Select(c=>c.CoveredMembers)))
.ToList();
....
I am making some assumptions about your data model here, and my code above probably needs a little tweaking.
EDIT:
I might need someone else to weigh in here, but I don't think you can add the where clause into an include like that (my example above leads you that way a bit by putting the include on the context object, instead return an IQueryable with your conditions set as solved in your first post (without a ToList() called on it) and then use the code you wrote above without the Where clauses:
From first post (you supplied different criteria in this one, but same concept)
var q = from q1 in dbContext.Parent
join q2 in dbContext.Children
on q1.key equals q2.fkey
join q3 in ........
where q4.col1 == 3000
select q1;
Then:
List<Person> people = q.Include(p => p.Plans
.Select(pl => pl.Coverages)
.Select(c => c.CoveredMembers).ToList();
Again, doing this without being able to troubleshoot - I am sure it would take me a few attempts to iron this one out too.
I have two collections in mongodb.I am retreiving data from two collections independently working gud.But when I am implementing paging using skip and take methods I am getting data from both the collections like this
paging = new Pagination() { CurrentPage = pageNumber, ItemsPerPage = 16 };
var results = dataTable.FindAs<TradeInfo(queryAll).Skip(paging.Skip).Take(paging.Take).ToList<TradeInfo>();
paging.TotalCount = Convert.ToInt32(dataTable.Find(query).Count());
var results2 = new List<TradeInfo>();
if (dataTable2 != null)
{
results2 = dataTable2.FindAs<TradeInfo(queryAll).Skip(paging.Skip).Take(paging.Take).ToList<TradeInfo>();
int count = Convert.ToInt32(dataTable2.Find(query).Count());
paging.TotalCount = paging.TotalCount + count;
results.AddRange(results2);
}
I am giving results as Itemssource to Datagrid and I am getting total 32 items per page.
How can I do that is there any joins concept in Mongodb.Two collections columns are same.
How can I do it?
Please help me in doing that....
Thanks,
jan
I believe what you are looking for here is more of a Union than a Join.
Unfortunately there is no such concept in MongoDB. If your paging is dependent on a query, which in this case it seems it might be, your only real option is to create and maintain a single merged collection which gets updated every time a document is added or saved to either of these two collections. Then you can skip and take on the single collection after applying the query to it.