I'm new to Linq. I've 2 tables Table 1 and Table 2. They are related by Id1.
Table 1 Table2
------- ------
Id1 Id2 RId1 (reference key from TAble 1)
1 1 1
2 1
2 3 2
4 2
5 Null
3 6 .
. 7 .
.
When I use the Where clause to query data from table 2, I get error Object reference not set to an instance of object
var result = db.Table2.Where(i => i.Rid1 == 1);
Even this code doesn't help
if (result != null)
Please help me.
In this case it appears that Rid1 is a nullable. Comparing a null against an integer may result in that error. Try changing it to the following:
db.Table2.Where(i => i.Rid1.GetValueOrDefault(0) == 1);
Related
Data:
ID PARENT_ID
1 [null]
2 1
3 1
4 2
Desired result:
ID CHILD_AT_ANY_LEVEL
1 2
1 3
1 4
2 4
I've tried SYS_CONNECT_BY_PATH, but I don't understand how to convert it result into "inline view" which I can use for JOIN with main table.
select connect_by_root(id) id, id child_at_any_level
from table
where level <> 1
connect by prior id = parent_id;
I am trying to create an ID based in multiple values in different columns in Power query.
The idea is to check the following values:
IF
ID_STORE = 1
ID_PRODUCT = 1
ID_CATEGORY = 1
SALE_DATE = 01/01/2018
ID_COSTUMER = 1
THEN CREATE THE SAME ID FOR THE ROWS THAT HAVE THIS INFO.
The idea is to check the rows that have that info (1 and 01/01/2018) in multiple columns (ID_STORE, ID_PRODUCT, ID_CATEGORY etc..).
Thanks in advance.
Obs: This is my first post, so feel free to correct me in any manner.
You need to add an 'AND' clause to your 'OF' statement;
if [ID_STORE] = 1
and [ID_PRODUCT] = 1
and [ID_CATEGORY] = 1
and [SALE_DATE] = Text.ToDate("01/01/2018")
and [ID_COSTUMER] = 1 then
1 else 0
I have one table scores where I have saving users scores. It's looks like this
table `scores`
id | points | user_id
1 5 1
2 2 1
3 4 1
4 1 3
5 10 2
I want to select each user, sum his points and show as a ranking. The result from above should be
user_id | points
1 11
2 10
3 1
The query with which I came up is
$sumPoints = Scores::select( \DB::raw("sum(points) as numberOfPoints"), \DB::raw("count(id) as numberId"))->groupBy("user_id")->first();
The problem is in ->first() because it's return only one result.. it is working as must. If I try to use ->get() instead I've got Undefined property error. How should I use this?
The query which is working in phpmyadmin
SELECT count(id) as numberId, sum(points) as numberOfPoints FROM `points` GROUP BY `user_id`
You can use something like this
$sumPoints = Scores::select( \DB::raw("sum(points) as numberOfPoints"), \DB::raw("count(id) as numberId"))->groupBy("user_id")->get();
foreach($sumPoints as $point){
dd($point); //OR dd($point->numberOfPoints)
}
NOTE
This might be a dup of this. But I don't get a clear answer from that.
The problem
I got wrong result from linq.
EXAMPLE
id groupid status name
------------------------------------
guid1 guidA reserved truck1
guid2 guidA reserved truck2
guid3 guidA reserved truck3
guid4 guidA reserved truck4
*assume all guids are guids..
**id is a primary key (unique)
CASE
If I put only where groupid == guidA the result is correct (4 rows)
but, if I put where groupid == guidA && status == reserved the result is wrong (3 rows)
EXPLANATION
The query built with expression tree. From the debug watch, the query (that return wrong the result) is like this
query.Expression:
-----------------
Convert(value(System.Data.Objects.ObjectSet`1[myEFTable]))
.MergeAs(AppendOnly)
.Where(m => ( m.groupId == value(myFilterClass).groupId))
.Where(m => m.status.Contains(value(myFilterClass).statusStr))
.Select(m => new myViewClass()
{
Id = m.id, GroupId = m.groupid, Status = m.status, Name = m.name
})
.OrderBy(o => o.Name).Skip(0).Take(10)
Then I tried to run a similar query and it returns correct result
assume e is ObjectSet<myEFTable> and strGuid is guidA
Guid grId = new Guid(strGuid);
e.AsQueryable()
.Where(m => m.status.Contains("reserved"))
.Where(m => m.groupId == grId)
.Select(m => new myViewClass()
{
Id = m.id, GroupId = m.groupid, Status = m.status, Name = m.name
}).OrderBy(o => o.Name).Skip(0).Take(10);
QUESTION
I'm completely clueless about this error..
If my EF tables are correct and the query is correct, why does it return wrong result?
Is it because the MergeAs(AppendOnly) ? because the only thing that different is that.
If this is about unique key, what should I do with myViewClass to ensure that every row is unique and should not be merged (if that was the case) ?
---------------------------------------------------------------------
UPDATE 2013/08/29
The result is incorrect because I have a typos in one of my query..
So, after changing few lot of here and there, try and error, till I almost lost the trace of whatever that changed, commented, erased, suddenly it works.. EUREKA!! what?
what I did is not really change everything, it's just a lot of changes but doesn't really end up so much different than where I was starting.. so there's that!
then that EUREKA moment ends and leave me tracing my way back to find out what is actually wrong, simply because I don't believe in miracles..
so here it is..
The tables is actually similar to this:
PartsGroups
-----------
id name
-----------
1 Nails
-----------
Items
-----------------
id name status
-----------------
2 Table Empty
5 Table Indent
6 Door Empty
3 Sofa Empty
PartsGroupPairs
------------------
id groupId partId
------------------
1 1 4
2 1 7
3 1 8
4 1 15
-------------------
Parts
------------------------
id name itemId status
------------------------
4 XNail 2 Empty
7 SNail 5 Empty
8 UNail 6 Empty
15 ZNail 3 Empty
------------------------
The relationships is like this
PartsGroups PartsGroupPairs Parts Items
----------- ------------------ ------------------------ -----------------
id name id groupId partId id name itemId status id name status
----------- ------------------ ------------------------ -----------------
1 Nails 1 1 4 4 XNail 2 Empty 2 Table Empty
1 Nails 2 1 7 7 SNail 5 Empty 5 Table Indent
1 Nails 3 1 8 8 UNail 6 Empty 6 Door Empty
1 Nails 4 1 15 15 ZNail 3 Empty 3 Sofa Empty
----------- ------------------- ------------------------ -----------------
One <---> Many Many <---> One Many <------> One
PartsGroup.pairs is a collection of PartsGroupPairs
PartsGroupPair.group is a PartsGroup
PartsGroupPair.part is a Part
Part.item is an Item
Item.parts is a collection of Parts
So when I select PartsGroup where name == 'Nails' it works perfectly, it returns 4 rows
But why when I select PartsGroup where name == 'Nails' and Status == 'Empty' it returns 3 rows?? (see below)
PartsGroups PartsGroupPairs Parts Items
----------- ------------------ ------------------------ -----------------
id name id groupId partId id name itemId status id name status
----------- ------------------ ------------------------ -----------------
1 Nails 1 1 4 4 XNail 2 Empty 2 Table Empty
1 Nails 3 1 8 8 UNail 6 Empty 6 Door Empty
1 Nails 4 1 15 15 ZNail 3 Empty 3 Sofa Empty
----------- ------------------- ------------------------ -----------------
this row didnt get selected..
PartsGroups PartsGroupPairs Parts Items
----------- ------------------ ------------------------ -----------------
id name id groupId partId id name itemId status id name status
----------- ------------------ ------------------------ -----------------
1 Nails 2 1 7 7 SNail 5 Empty 5 Table Indent
----------- ------------------- ------------------------ -----------------
the mistake I made is at the Where part. The query itself built at the runtime coz I separate entities, filters, views and paging modules. So mostly I just passing IQueryable here and there.
In the case for filter, every time I filter, I'll add another Where. So in this case it went like this below:
using(var DB = new databaseContext())
{
ObjectSet<PartsGroupPair> d =
DB.CreateObjectSet<PartsGroupPair>("partsGroupPair");
int searchGroupId = 1; // int instead of guid for example
int searchStatus = "Empty";
// filter by specific PartsGroup
IQueryable<PartsGroupPair> e = d.Where(m => m.group.id == searchGroupId);
// then if I want to filter by the status
e = e.Where(m => m.part.item.status == searchStatus)); // WRONG!!
// I want to filter by part.status, not item.status
// so instead, it should be
e = e.Where(m => m.part.status == searchStatus)); // RIGHT!!
// view
IQueryable<PartsGroupPairView> f =
e.Select(m => new PartsGroupPairView()
{
Id = m.id, GroupId = m.groupid,
Status = m.part.status, Name = m.part.name
// etc..
});
// paging
f = f.OrderBy(o => o.Name).Skip(0).Take(10);
}
The wrong filtering makes LINQ ignore the other Parts, and returns 3 rows instead of 4 because it found only one Item instead of 2 Parts.
So in my case, it's a silly typo with a quite complex data..
It's really frustrating when nothing works while everything seems to be okay..
I need return a query where all the unique page numbers are returned with the max version number of each page.
Here is the an example of the data that I'd query
DocumentID PageNumber Version
1 1 1
1 2 1
1 2 2
1 3 1
1 3 2
1 3 3
And here is what I would need to get returned in my query
DocumentID PageNumber Version
1 1 1
1 2 2
1 3 3
Not sure how to finish this:
var pages = from p in dc.Pages where p.DocumentID == 1 && ...
I think this is what you're trying to achieve:
var results =
from p in dc.Pages
where p.DocumentID == 1
group p by p.PageNumber into g
select new
{
PageNumber = g.Key,
MaxVersion = g.Max(x => x.Version)
};
This query may help you:
Select DocumentID ,Distinct PageNumber, max(version) from table
group by DocumentID, Distinct PageNumber