Can I get some help diagnosing the following?
IQueryable<MyComponentsViewModel> vcvm = from v1 in pg.MyComponents
join item in Items on v1.Item equals item into vc
select new MyComponentsViewModel
{ Cost = item.Cost };
The following error appears:
Error CS1941: The type of one of the expressions in the join clause is
incorrect. Type inference failed in the call to 'GroupJoin'.
Is this error state occuring as item is not the same type as v1.Item?
The keys are shown below
ALTER TABLE [dbo].[MyComponents] WITH CHECK ADD CONSTRAINT
[FK_MyComponents_Items] FOREIGN KEY([ItemId])
REFERENCES [dbo].[Items] ([Itemid])
GO
ALTER TABLE [dbo].[MyComponents] CHECK CONSTRAINT [FK_MyComponents_Items]
I assume like, you need inner join and while you doing equals you need to use their matching column Ids to filter records like below
IQueryable<MyComponentsViewModel> vcvm =
from myComp in pg.MyComponents
join item in Items on myComp.ItemId equals item.Id
select new MyComponentsViewModel { Cost = item.Cost };
I was able to get it to work.
There was an ambiguity between an action named Items. Fully specify the namespace resolved this.
Additionally I had to add the statement "from subitem in vc.DefaultIfEmpty"
I'm still working to learn the full semantics of this
IQueryable<MyComponentsViewModel> vcvm =
from v1 in pg.MyComponents
join item in pg.Items on v1.Item equals item into vc
from subitem in vc.DefaultIfEmpty()
select new MyComponentsViewModel { Cost = subitem.Cost };
Related
I have created a CDS views as follows:
define view YGAC_I_REQUEST_ROLE
with parameters
pm_req_id : grfn_guid,
#Consumption.defaultValue: 'ROL'
pm_item_type : grac_prov_item_type,
#Consumption.defaultValue: 'AP'
pm_approval : grac_approval_status
as select from YGAC_I_REQ_PROVISION_ITEM as provitem
association [1..1] to YGAC_I_ROLE as _Role on _Role.RoleId = provitem.ProvisionItemId
association [1..*] to YGAC_I_ROLE_RS as _Relation on _Relation.RoleId1 = provitem.ProvisionItemId
{
key ReqId,
key ReqIdItem,
Connector,
ProvisionItemId,
ActionType,
ValidFrom,
ValidTo,
_Role.RoleId,
_Role.RoleName,
_Role.RoleType,
_Role,
_Relation
}
where
ReqId = $parameters.pm_req_id
and ProvisionItemType = $parameters.pm_item_type
and ApprovalStatus = $parameters.pm_approval
Then I have consumed in ABAP:
SELECT
FROM ygac_i_request_role( pm_req_id = #lv_test,
pm_item_type = #lv_item_type,
pm_approval = #lv_approval
)
FIELDS reqid,
connector,
provisionitemid
INTO TABLE #DATA(lt_result).
How to get the list of _Relation according to selection above.
This is generally not possible like in ABAP SQL queries:
SELECT m~*, kt~*
FROM mara AS m
JOIN makt AS kt
...
This contradicts the whole idea of CDS associations, because they were created to join on-demand and to reduce redundant calls to database. Fetching all fields negates the whole idea of "lazy join".
However, there is another syntax in FROM clause which is enabled by path expressions that allows querying underlining associations both fully and by separate elements. Here is how
SELECT *
FROM ygac_i_request_role( pm_req_id = #lv_test )
\_Role AS role
INTO TABLE #DATA(lt_result).
This fetches all the fields of _Role association into internal table.
Note: remember, it is not possible to fetch all the published associations of current view simultaneously, only one path per query.
Possible workaround is to use JOIN
SELECT *
FROM ygac_i_request_role AS main
JOIN ygac_i_request_role
\_Role AS role
ON main~ProvisionItemId = role~RoleId
JOIN ygac_i_request_role
\_Relation AS relation
ON main~ProvisionItemId = relation~RoleId1
INTO TABLE #DATA(lt_table).
This creates deep-structured type with dedicated structure for every join association like this:
If you are not comfortable with such structure for you task, lt_table should be declared statically to put up all the fields in a flat way
TYPES BEGIN OF ty_table.
INCLUDE TYPE ygac_i_request_role.
INCLUDE TYPE ygac_i_role.
INCLUDE TYPE ygac_i_role_rs.
TYPES END OF ty_table.
I am comming to ASP .NET Core from PHP w/ MySQL.
The problem:
For the illustration, suppose the following two tables:
T: {ID, Description, FK} and States: {ID, ID_T, Time, State}. There is 1:n relationship between them (ID_T references T.ID).
I need all the records from T with some specific value of FK (lets say 1) along with the related newest record in States (if any).
In terms of SQL it can be written as:
SELECT T.ID, T.Description, COALESCE(s.State, 0) AS 'State' FROM T
LEFT JOIN (
SELECT ID_T, MAX(Time) AS 'Time'
FROM States
GROUP BY ID_T
) AS sub ON T.ID = sub.ID_T
LEFT JOIN States AS s ON T.ID = s.ID_T AND sub.Time = s.Time
WHERE FK = 1
I am struggling to write an efficient equivalent query in LINQ (or the fluent API). The best working solution I've got so far is:
from t in _context.T
where t.FK == 1
join s in _context.States on t.ID equals o.ID_T into _s
from s in _s.DefaultIfEmpty()
let x = new
{
id = t.ID,
time = s == null ? null : (DateTime?)s.Time,
state = s == null ? false : s.State
}
group x by x.id into x
select x.OrderByDescending(g => g.time).First();
When I check the resulting SQL query in the output window when executed it is just like:
SELECT [t].[ID], [t].[Description], [t].[FK], [s].[ID], [s].[ID_T], [s].[Time], [s].[State]
FROM [T] AS [t]
LEFT JOIN [States] AS [s] ON [T].[ID] = [s].[ID_T]
WHERE [t].[FK] = 1
ORDER BY [t].[ID]
Not only it selects more columns than I need (in the real scheme there are more of them). There is no grouping in the query so I suppose it selects everything from the DB (and States is going to be huge) and the grouping/filtering is happening outside the DB.
The questions:
What would you do?
Is there an efficient query in LINQ / Fluent API?
If not, what workarounds can be used?
Raw SQL ruins the concept of abstracting from a specific DB technology and its use is very clunky in current Entity Framework Core (but maybe its the best solution).
To me, this looks like a good example for using a database view - again, not really supported by Entity Framework Core (but maybe its the best solution).
What happens if you try to do a more straight forward translation to LINQ?
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID_T = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID_T into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States on new { t.ID, sub.Time } equals new { s.ID, s.Time } into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? 0 : s.State) };
Apparently the ?? operator will translate to COALESCE and may handle an empty table properly, so you could replace the select with:
select new { t.ID, t.Description, State = s.State ?? 0 };
OK. Reading this article (almost a year old now), Smit's comment to the original question and other sources, it seems that EF Core is not really production ready yet. It is not able to translate grouping to SQL and therefore it is performed on the client side, which may be (and in my case would be) a serious problem. It corresponds to the observed behavior (the generated SQL query does no grouping and selects everything in all groups). Trying the LINQ queries out in Linqpad it always translates to a single SQL query.
I have downgraded to EF6 following this article. It required some changes in my model's code and some queries. After changing .First() to .FirstOrDefault() in my original LINQ query it works fine and translates to a single SQL query selecting only the needed columns. The generated query is much more complex than it is needed, though.
Using a query from NetMage's answer (after small fixes), it results in a SQL query almost identical to my own original SQL query (there's only a more complex construct than COALESCE).
var latestState = from s in _context.States
group s by s.ID_T into sg
select new { ID = sg.Key, Time = sg.Time.Max() };
var ans = from t in _context.T
where t.FK == 1
join sub in latestState on t.ID equals sub.ID into subj
from sub in subj.DefaultIfEmpty()
join s in _context.States
on new { ID_T = t.ID, sub.Time } equals new { s.ID_T, s.Time }
into sj
from s in sj.DefaultIfEmpty()
select new { t.ID, t.Description, State = (s == null ? false : s.State) };
In LINQ it's not as elegant as my original SQL query but semantically it's the same and it does more or less the same thing on the DB side.
In EF6 it is also much more convenient to use arbitrary raw SQL queries and AFAIK also the database views.
The biggest downside of this approach is that full .NET framework has to be targeted, EF6 is not compatible with .NET Core.
I have an ASP.NET Web API app using Oracle's Entity Framework driver. I have an entity defined for a view as follows:
CREATE OR REPLACE FORCE VIEW "PHASE_TWO"."EDIPRODUCT" ("ID", "STK_NUM", "TITLE", "ISBN", "UPC", "ITEMNO", "LONGFORMAT", "ABRIDGED", "WEB_TITLES_ID", "OCLC", "GENRE", "RELYEAR", "ORIG_REL", "LANG", "ORIG_STKNUM", "PUBLISHER", "PEOPLELIST", "SALES_ORG", "NOT_AVAIL") AS
SELECT sap_product.id,
sap_product.stk_num,
sap_product.longdesc AS title,
sap_product.isbn,
sap_product.upc,
sap_product.itemno,
sap_product.longformat,
sap_product.abridged,
mwt_product.web_titles_id,
mwt_product.oclc,
mwt_product.genre,
mwt_product.RELYEAR,
sap_product.orig_rel,
sap_product.lang,
sap_product.orig_stknum,
UPPER (publisher.name) publisher,
(SELECT LISTAGG (p.FULLNAME, ', ') WITHIN GROUP (
ORDER BY pp.rank) AS People
FROM people p
JOIN product_people pp
ON p.id = pp.peopleid
WHERE pp.stk_num = sap_product.stk_num
GROUP BY pp.STK_NUM
) PeopleList,
sppg.PRICING_TYPE as sales_org,
sap_product.not_avail
FROM sap_product
JOIN mwt_product ON sap_product.stk_num = mwt_product.stk_num
JOIN publisher ON mwt_product.publisherid = publisher.id
JOIN SAP_PRODUCT_PRICING_GROUP sppg on sppg.STK_NUM = mwt_product.stk_num and sppg.MARKED_FOR_DELETION = 0
WHERE mwt_product.WEB_PRODUCTS_ID > 0;
This view works as expected in SQL Developer. My getEDIPRODUCT function (yes, it's VB.NET) in my controller is as follows:
' GET: odata/EDIPRODUCTs
<EnableQuery>
Function GetEDIPRODUCT() As IQueryable(Of EDIPRODUCT)
Dim results As IQueryable
results = db.EDIPRODUCT
For Each _product In results
Console.Write(_product)
Next
Return results
End Function
I just added the for loop in order to inspect the results. What I see when I inspect the results is the same product record is returned for each row. The value for the ID is duplicate and the only other field that should have variant values (sppg.PRICING_TYPE as sales_org) also just repeats.
I have other views where this does not occur. The correct number of records are always returned, but the first record retrieved is always just repeated in each row of the result set. Any idea what could be going on here?
I never actually resolved this issue and am still interested in why this fails, but I rewrote the portion of the app that uses this view to use OData's $expand to retrieve the related data.
I have three tables: Schools (id, school_name), Schools_Focuses (id, school_id, focus_id) and Focuses (id, focus) and want to create a method on my Schools model that returns all related Focuses.
I can perform what I want to do with this SQL QUERY:
SELECT focus FROM focuses INNER JOIN schools_focuses ON focuses.id = schools_focuses.focus_id INNER JOIN schools ON schools.id = schools_focuses.school_id WHERE schools.id = 36;
Model code:
// Define Models
exports.School = School = Bookshelf.PG.Model.extend({
tableName: 'schools',
focuses: function() {
return this.hasMany(Focus).through(Schools_Focuses);
}
});
Error:
Possibly unhandled Error: column focuses.schools_focuse_id does not exist, sql: select "focuses".*, "schools_focuses"."id" as "_pivot_id", "schools_focuses"."school_id" as "_pivot_school_id" from "focuses" inner join "schools_focuses" on "schools_focuses"."id" = "focuses"."schools_focuse_id" where "schools_focuses"."school_id" in (?)
I don't want to have this extra column (focuses.schools_focuse_id) in Focuses because a focus can belongTo more than one school.
How can I correctly set this up? I have played around with the foreign keys and other keys for hasMany() and through() but no luck.
Thanks!
Sounds like you need to use belongsToMany() instead of hasMany().
// Define Models
exports.School = School = Bookshelf.PG.Model.extend({
tableName: 'schools',
focuses: function() {
return this.belongsToMany(Focus, 'schools_focuses');
}
});
The second parameter is needed since the join table isn't in alpha order ('focuses_schools'). And if it has problems identifying the join keys (school_id, focus_id) you can override those as parameters as well. Also, since it uses the join table internally, you don't need to create a separate model for Schools_Focuses.
If we don't need to create a separate model for Schools_Focuses, then how do we query data from the junction table i.e:
'SELECT * FROM focuses_schools WHERE focus_id = 2 & school_id = 1'
Actually I spend whole day on the EntityFramework for foreign key.
assume we have two table.
Process(app_id,process_id)
LookupProcessId(process_id, process_description)
you can understand two tables with names, first table ,use process_id to indicate every application, and description is in the seoncd table.
Actually i try many times and figure out how to do inquery: it was like
Dim result = (from x in db.Processes where x.LookupProcess is (from m in db.LookupProcessIds where descr = "example" select m).FirstOrDefault() select x).FirstOrDefault()
First I want to ask is there easier way to do it.
Second i want to ask question is about insert
p As New AmpApplication.CUEngData.Process
p.app_id=100
p.LookupProcess = (from m in db.LookupProcessIds where descr = "example" select m).FirstOrDefault()
db.AddToProcesses(p)
db.SaveChanges()
from appearance it looks fine, but it give me error says
Entities in 'AmpCUEngEntities.Processes' participate in the 'FK_Process_LookupProcess' relationship. 0 related 'LookupProcess' were found. 1 'LookupProcess' is expected.
can i ask is that insert wrong? and is that my query correct?
For your first question:
Dim result = (from x in db.Processes
where x.LookupProcess.descr = "example"
select x).FirstOrDefault()
Actually, you missed some concepts from DataEntityModel, and its Framework. To manipulate data, you have to call object from contextual point of view. Those allow you to specify to the ObjectStateManager the state of an DataObject. In your case, if you have depending data from FK, you will have to add/update any linked data from leaf to root.
This example demonstrate simple (no dependances) data manipulation. A select if existing and an insert or update.
If you want more info about ObjectStateManager manipulation go to http://msdn.microsoft.com/en-us/library/bb156104.aspx
Dim context As New Processing_context 'deseign your context (this one is linked to a DB)
Dim pro = (From r In context.PROCESS
Where r.LOOKUPPROCESS.descr = LookupProcess.descr
Select r).FirstOrDefault()
If pro Is Nothing Then 'add a new one
pro = New context.PROCESS With {.AP_ID = "id", .PROCESS_ID = "p_id"}
context.PROCESS.Attach(pro)
context.ObjectStateManager.ChangeObjectState(pro, System.Data.EntityState.Added)
Else
'update data attibutes
pro.AP_ID = "id"
pro.PROCESS_ID = "p_id"
context.ObjectStateManager.ChangeObjectState(pro, System.Data.EntityState.Modified)
'context.PROCESS.Attach(pro)
End If
context.SaveChanges()
I hope this will help. Have a nice day!
For your first question, to expand on what #jeroenh suggested:
Dim result = (from x in db.Processes.Include("LookupProcess")
where x.LookupProcess.descr = "example"
select x).FirstOrDefault()
The addition of the Include statement will hydrate the LookupProcess entities so that you can query them. Without the Include, x.LookupProcess will be null which would likely explain why you got the error you did.
If using the literal string as an argument to Include is not ideal, see Returning from a DbSet 3 tables without the error "cannot be inferred from the query" for an example of doing this using nested entities.
For your second question, this line
p.LookupProcess = (from m in db.LookupProcessIds
where descr = "example" select m).FirstOrDefault()
Could cause you problems later on because if there is no LookupProcessId with a process_description of "example", you are going to get null. From MSDN:
The default value for reference and nullable types is null.
Because of this, if p.LookupProcess is null when you insert the entity, you will get the exception:
Entities in 'AmpCUEngEntities.Processes' participate in the 'FK_Process_LookupProcess' relationship. 0 related 'LookupProcess' were found. 1 'LookupProcess' is expected.
To avoid this kind of problem, you will need to check that p.LookupProcess is not null before it goes in the database.
If Not p.LookupProcess Is Nothing Then
db.AddToProcesses(p)
db.SaveChanges()
End If