I'm having problems with a LINQ to SQL query in the following scenario:
I have items that have "Tags" applied via a bridge table.
I'm trying to filter a list of items to a subset that contain all of a specified set of tags and return the filtered list of items as the query result.
Tables Involved:
Item (ItemId, Name, ...other fields)
Tag (TagId, TagName)
Item_Tag(ItemId, TagId)
As an example if I had a list of Items with tags:
Item1 w/ (Tag1, Tag2)
Item2 w/ (Tag1, Tag2)
Item3 w/ (Tag1)
and I wanted to get all items where the item has both Tag1 AND Tag2 where the filter requirement is provided as an int[] of the required tagIds.
Assuming the Item and Tag Id's match the number at the end of the name. The filter for this example would be:
int[] tagFilterConditions = int[2]{1, 2};
var query = from i in itemList
//define filter here
where the result would be:
Item1,Item2 (excludes Item 3 b/c it isn't tagged with Tag1 AND Tag2)
I'm having a tough time figuring out how to combine these tables to apply that filter on the source list, I've tried using a predicate builder and various joins but just can't get the correct results.
Thanks, for any help...
// Query for all the items in the list
int[] itemIds = itemList.Select(item => item.ItemId).AsArray();
var query =
db.Item.Where(item =>
itemIds.Contains(item.ItemId));
// Apply each tag condition
foreach (int tagid in tagFilterConditions)
{
int temp = tagid;
query = query.Where(item =>
db.Item_Tag.Exists(item_tag =>
item_tag.ItemId == item.ItemId && item_tag.TagId == temp)));
}
I think the answer to your question is in .Contains(): http://blog.wekeroad.com/2008/02/27/creating-in-queries-with-linq-to-sql
Here's what I think is the relevant snippet from that site to your question:
int[] productList = new int[] { 1, 2, 3, 4 };
var myProducts = from p in db.Products
where productList.Contains(p.ProductID)
select p;
Hope this helps!
Here is some sql.
and here is the LinqToSql..
Got the following query to work using an anonymous type after defining the proper foreign key relationships the query was adapted from an answer on this question.
//the tagId's that the item in itemList must have
int[] tagFilterConditions = int[2]{1, 2};
var query =
itemList.Select( i=> new { i, itemTags= item.Item_Tags.Select(it=> it.TagId)})
.Where( x=> tagFilterConditions.All( t=> x.itemTags.Contains(t)))
.Select(x=> x.s);
Related
I am very unfamiliar with Entity Framework and LINQ. I have a single entity set with some columns where I want to filter our some special rows.
4 of the rows are named Guid (string), Year (short), Month (short) and FileIndex (short). I want to get all rows which have the maximum FileIndex for each existing combination of Guid-Year-Month.
My current solution looks like this:
var maxFileIndexRecords = from item in context.Udps
group item by new { item.Guid, item.Year, item.Month }
into gcs
select new { gcs.Key.Guid, gcs.Key.Year, gcs.Key.Month,
gcs.OrderByDescending(x => x.FileIndex).FirstOrDefault().FileIndex };
var result = from item in context.Udps
join j in maxFileIndexRecords on
new
{
item.Guid,
item.Year,
item.Month,
item.FileIndex
}
equals
new
{
j.Guid,
j.Year,
j.Month,
j.FileIndex
}
select item;
I think there should be a shorter solution with more performance. Does anyone have a hint for me?
Thank you
You were close. It's not necessary to actually select the grouping key. You can simply select the first item of each group:
var maxFileIndexRecords =
from item in context.Udps
group item by new { item.Guid, item.Year, item.Month }
into gcs
select gcs.OrderByDescending(x => x.FileIndex).FirstOrDefault();
I have a List of ints. I need to select elements from a data source where a particular field/column matches each int in the list.
Data Source Example
ItemID ListID
1 1
1 2
2 1
I want to find all Items that match all ListIDs from a List containing List IDs 1 and 2.
Currently I'm using...
List<Item> items = (from element in MyItems where listIDs.Contains(element.ListID) select element).ToList();
However, this produces an OR query and not an AND query across multiple rows for each distinct ItemID.
You can try this way :
List<Item> result = MyItems.GroupBy(o => o.ItemID)
//find group that contain all listIDs
.Where(o => !listIDs.Except(o.Select(x => x.ListID)).Any())
//flatten groups to items
.SelectMany(o => o)
.ToList();
Related question : Determine if a sequence contains all elements of another sequence using Linq
If you are trying to compare two list for equality, then you could use SequenceEqual method.
Something along the lines
list<item> results = (from element in MyItems where listIDs.SequenceEqauls(element.ListID) select element).ToList();
I am not entirely sure if I understood your question properly. When you say "particular field/column," is that field/column some kind of collection as well?
if i got your question !! then try this
var MyItems=<your data column values>
var ItemsMatch=MyItems.Where(z=>MyIntsList.Contains(int.Pars(z.ToString()))).ToArray();
I'm not sure I understand the question. I think you have a list and you are trying to match rows that have both ListID & ItemID equal to ANY item in the list. If thats what you are sking this this is a way to do it:
List<Item> items = from element in MyItems
where listIDs.Contains(element.ListID) and listIDs.Contains(element.ItemID)
Or perhaps you are trying to match rows that have both ListID & ItemID equal to the SAME item in the list. If thats what you are sking this this is a way to do it:
List<Item> items = from element in MyItems
where listIDs.Contains(element.ListID) and element.ListID == element.ItemID
If i understood you correctly,this will do:
var result = (from item in MyItems
from i in listIDs
where i == item.ListId
select item).ToList();
It will get all Item objects in MyItems list that have ListId present in ListId.
I am having at hierarchical table with the structure
ID, Name, FK_ID, Sortkey
Fetching the data in LINQ to SQL is straight forward:
var list = from ls in db.myTable
where ls.FK_ID == levelId
orderby ls.sortkey ascending
select ls;
And I can traverse down the tree by linking to the next levelId.
But what I can't figure out, if there is a way in LINQ, to check if there is any children
I could probably build a view, that added a flag to each record, but I would rather do this in LINQ, if possible.
What would even be the best practice for adding such a flag in SQL?
My idea on checking each record, is not the most performance friendly solution.
If you have set up the foreign key correctly, should you not have the 1 to Many mapping properties?
i.e. You could write
var listWithChildren = list.Where(l => l.Children.Any());
or going the other direction
var listWithParent = list.Where(l => l.FK_ID != null);
or using the query expression instead of fluent
var listWithChildren = from item in list
where item.Children.Any()
select item;
as you asked in your comments for a boolean flag, you could do
var updatedList = from item in list
select new
{
Item = item,
HasChildren = item.Children.Any()
};
I need to retrieve a list of entities from my database that matches a list of items in a plain list (not EF). Is this possible with Entity Framework 4.1?
Example:
var list = new List<string> { "abc", "def", "ghi" };
var items = from i in context.Items
where list.Contains(i.Name)
select i;
This works great to return rows that match one property, but I actually have a more complex property:
var list = new List<Tuple<string, string>>
{
new Tuple<string,string>("abc", "123"),
new Tuple<string,string>("def", "456")
};
// i need to write a query something like this:
var items = from i in context.Items
where list.Contains(new Tuple<string,string>(i.Name, i.Type))
select i;
I know that is not valid because it will say it needs to be a primitive type, but is there any way to do what I'm trying to accomplish or will I need to resort to a stored procedure?
You have a few options:
1) You could, of course, write a stored procedure to do what you need and call it.
2) You could read the table into memory and then query the in memory list...that way you don't have to use primitives:
var items = from i in context.Items.ToList()
where list.Contains(new Tuple<string, string>(i.Name, i.Type))
select i;
3) You could also convert your query to use primitives to achieve the same goal:
var items = from i in context.Items
join l in list
on new { i.Name, i.Type } equals
new { Name = l.Item1, Type = l.Item2 }
select i;
I would go with the second option as long as the table isn't extremely large. Otherwise, go with the first.
You need to break it down to sub-properties. For example, something like (this might not compile, i'm not able to test at the moment, but it should give you something to work with):
var items = from i in context.Items
where list.Select(x => x.Item1).Contains(i.Name)
&& list.Select(x => x.Item2).Contains(i.Type)
select i;
You have to think about what the resulting SQL would look like, this would be difficult to do directly in SQL.
My suggestion would be you split out one field of the tuples and use this to cut down the results list, get back the query result then filter again to match one of the tuples e.g.
var list = new List<string> { "abc", "def" };
var list2 = new List<Tuple<string, string>>
{
new Tuple<string,string>("abc", "123"),
new Tuple<string,string>("def", "456")
};
var items = (from i in context.Items
where list.Contains(i.Name)
select i)
.AsEnumerable()
.Where(i => list2.Any(j => j.val1 == i.Name && j.val2 == i.Type);
I have a known list of strings like the following:
List<string> groupNames = new List<string>(){"Group1","Group2","Group3"};
I also have a list of strings that is not known in advance that will be something like this:
List<string> dataList = new List<string>()
{
"Group1.SomeOtherText",
"Group1.SomeOtherText2",
"Group3.MoreText",
"Group2.EvenMoreText"
};
I want to do a LINQ statement that will take the dataList and convert it into either an anonymous object or a dictionary that has a Key of the group name and a Value that contains a list of the strings in that group. With the intention of looping over the groups and inner looping over the group list and doing different actions on the strings based on which group it is in.
I would like a data structure that looks something like this:
var grouped = new
{
new
{
Key="Group1",
DataList=new List<string>()
{
"Group1.SomeOtherText",
"Group1.SomeOtherText2"
}
},
new
{
Key="Group2",
DataList=new List<string>()
{
"Group2.EvenMoreText"
}
}
...
};
I know I can just loop through the dataList and then check if each string contains the group name then add them to individual lists, but I am trying to learn the LINQ way of doing such a task.
Thanks in advance.
EDIT:
Just had another idea... What if my group names were in an Enum?
public enum Groups
{
Group1,
Group2,
Group3
}
How would I get that into a Dictionary>?
This is what I am trying but i am not sure how to form the ToDictionary part
Dictionary<Groups,List<string>> groupedDictionary = (from groupName in Enum.GetNames(typeof(Groups))
from data in dataList
where data.Contains(groupName)
group data by groupName).ToDictionary<Groups,List<string>>(...NOT SURE WHAT TO PUT HERE....);
EDIT 2:
Found the solution to the Enum question:
var enumType = typeof(Groups);
Dictionary<Groups,List<string>> query = (from groupName in Enum.GetValues(enumType).Cast<Groups>()
from data in dataList
where data.Contains(Enum.GetName(enumType, groupName))
group data by groupName).ToDictionary(x => x.Key, x=> x.ToList());
That looks like:
var query = from groupName in groupNames
from data in dataList
where data.StartsWith(groupName)
group data by groupName;
Note that this isn't a join, as potentially there are overlapping group names "G" and "Gr" for example, so an item could match multiple group names. If you could extract a group name from each item (e.g. by taking everything before the first dot) then you could use "join ... into" to get a group join. Anyway...
Then:
foreach (var result in query)
{
Console.WriteLine("Key: {0}", result.Key);
foreach (var item in result)
{
Console.WriteLine(" " + item);
}
}
If you really need the anonymous type, you can do...
var query = from groupName in groupNames
from data in dataList
where data.StartsWith(groupName)
group data by groupName into g
select new { g.Key, DataList = g.ToList() };