I have three tables that I would like to query: Streams, Entries, and FieldInstances.
I'm wanting to get a list of entries inside a stream. A Stream could be a blog or a page etc. and entry is the actual instance of the stream ie: "stream:Page entry:Welcome" or "stream:blog entry:News about somthing".
The thing is, each entry has custom data field associated with it through FieldInstance. IE:
stream: Page
entry: Welcome
fieldInstance: Welcome Image Path
I'm trying to figure out the best way to get a list of all entries inside of one stream and also have the custom field instances that are associated with each entry.
I've been playing around with code like this:
var stream = genesisRepository.Streams.First(x => x.StreamUrl == streamUrl);
IQueryable<StreamEntry> entry = genesisRepository.StreamEntries.Where(x => x.StreamID == stream.StreamID);
IQueryable<FieldInstance> fieldInstances = genesisRepository.FieldInstances.Where(
// doesn't work because entry is basically returning a collection of some kind.
// and i can't figure out how to compare a single ID with a list/collection of IDs
x => x.fiStreamEntryID == entry.Where(e => e.StreamID == stream.StreamID)
);
This of course doesn't work. Inititially I was thinking to get all entries in the stream and then all fieldInstances in the stream, then I'll display the data using lambdas after I have everything... hopefully keeping sql queries dows to two or three. But I can't figure out how to write the linqTOsql to execute in just two or three queries. I keep thinking that I need to execute queries in a loop to get the fieldInstances for each entry.
Is there a LinqTOsql query that will select all fieldInstances where the StreamEntryID(fk) is in the list of entries whose (fk)StreamID matches the Stream?
Sorry, I don't quite get what columns you are joining in the third statement, but:
var stream = genesisRepository.Streams.First(x => x.StreamUrl == streamUrl);
IQueryable<StreamEntry> entries = genesisRepository.StreamEntries.Where(x => x.StreamID == stream.StreamID);
IQueryable<FieldInstance> fieldInstances = from entry in entries
from instance in genesisRepository.FieldInstances
where entry.entryId == instance.fiStreamEntryID
select instance;
Does this help? I'm still new to EF but that's how I'd have a crack at it...
var results = genesisRepository.FieldInstances
.Include("StreamEntry.Stream")
.Where(fi => fi.StreamEntry.Stream.StreamUrl == streamUrl);
Related
I'm make quiz app on flutter and have local json with
questions(around 200). How i can limit questions for 40?
because when i open app its show me all question
json={results:[
{question},
]}
final jsonResponse = convert.jsonDecode(json);
final result = (jsonResponse['results'] as List).map((question)
=> QuestionModel.fromJson(question));
questions.value =
result.map((question) =>
Question.fromQuestionModel(question)).toList();
return true;
}
}
Use subList function after using .toList().
this can be done easily by using .subList() which basically returns a list from the start index to the end index parameters from your original List ,like this
final result = (jsonResponse['results'] as List).map((question)
=> QuestionModel.fromJson(question));
questions.value =
result.map((question) =>
Question.fromQuestionModel(question)).toList().sublist(0,39);
Note
if you want to save all the 200 Questions and get every 40 questions then you should use pagination ,in this case you'll not use the subList function here, you'll use it after returning the result with the list that should be attached with the ui part.
Bonus Tip
check out this flutter plugin flutter page wise which makes the pagination alot easier, it can very helpful in a lot of situations.
I have 2 tables that I need to load together all the time, the both must exist together in the database. However I am wondering why Linq to Sql demands that I have to load in a collection and then do a join, I only want to join 2 single tables where a record where paramid say = 5, example...
var data = _repo.All<TheData>(); //why do I need a collection/IQueryable like this?
var _workflow = _repo.All<WorkFlow>()
.Where(x => x.WFID== paramid)
.Join(data, x => x.ID, y => y.WFID, (x, y) => new
{
data = x,
workflow = y
});
I gues then I need to do a SingleOrDefault()? If the record is not null pass it back?
I Understand the Sql query comes out correctly, is there a better way to write this?
NOTE: I need to search a table called Participants to see if the loggedonuser can actually view this record, so I guess I should leave it as this? (this is main requirement)
var participant = _repo.All<Participants>();
.Any(x=> x.ParticipantID == loggedonuser.ID); //add this to above query...
The line var data = _repo.All<TheData>(); is something like saying 'start building query against the TheData table'.
This function returns you an IQueryable which will contain a definition of the query against your database.
So this doesn't mean you load the whole TheData table data with this line!
The query will be executed the moment you do something like .Count(), .Any(), First(), Single(), or ToList(). This is called deferred execution.
If you would end your query with SingleOrDefault() this will create a sql query that joins the two tables, add the filter and select the top most record or null(or throw an error if there are more!).
You could also use Linq instead of query extension methods.
It would look like:
var data = _repo.All<TheData>();
var _workflow = from w in _repo.All<WorkFlow>()
join t in _repo.All<TheData> on w.Id equals t.WFID
where x.WIFD = paramid
select new
{
data = t,
workflow = x
});
I am trying to get the records from the 'many' table of a one-to-many relationship and add them as a list to the relevant record from the 'one' table.
I am also trying to do this in a single database request.
Code derived from Linq to Sql - Populate JOIN result into a List almost achieves the intended result, but makes one database request per entry in the 'one' table which is unacceptable. That failing code is here:
var res = from variable in _dc.GetTable<VARIABLE>()
select new { x = variable, y = variable.VARIABLE_VALUEs };
However if I do a similar query but loop through all the results, then only a single database request is made. This code achieves all goals:
var res = from variable in _dc.GetTable<VARIABLE>()
select variable;
List<GDO.Variable> output = new List<GDO.Variable>();
foreach (var v2 in res)
{
List<GDO.VariableValue> values = new List<GDO.VariableValue>();
foreach (var vv in v2.VARIABLE_VALUEs)
{
values.Add(VariableValue.EntityToGDO(vv));
}
output.Add(EntityToGDO(v2));
output[output.Count - 1].VariableValues = values;
}
However the latter code is ugly as hell, and it really feels like something that should be do-able in a single linq query.
So, how can this be done in a single linq query that makes only a single database query?
In both cases the table is set to preload using the following code:
_dc = _db.CreateLinqDataContext();
var loadOptions = new DataLoadOptions();
loadOptions.LoadWith<VARIABLE>(v => v.VARIABLE_VALUEs);
_dc.LoadOptions = loadOptions;
I am using .NET 3.5, and the database back-end was generated using SqlMetal.
This link may help
http://msdn.microsoft.com/en-us/vcsharp/aa336746.aspx
Look under join operators. You'll probably have to change from using extension syntax other syntax too. Like this,
var = from obj in dc.Table
from obj2 in dc.Table2
where condition
select
Follow up to this question. I have the following code:
string[] names = new[] { "Bob", "bob", "BoB" };
using (MyDataContext dataContext = new MyDataContext())
{
foreach (var name in names)
{
string s = name;
if (dataContext.Users.SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
dataContext.Users.InsertOnSubmit(new User { Name = name });
}
dataContext.SubmitChanges();
}
...and it inserts all three names ("Bob", "bob" and "BoB"). If this was Linq-to-Objects, it wouldn't.
Can I make it look at the pending changes as well as what's already in the table?
I don't think that would be possible in general. Imagine you made a query like this:
dataContext.Users.InsertOnSubmit(new User { GroupId = 1 });
var groups = dataContext.Groups.Where(grp => grp.Users.Any());
The database knows nothing about the new user (yet) because the insert wasn't commited yet, so the generated SQL query might not return the Group with Id = 1. The only way the DataContext could take into account the not-yet-submitted insert in cases like this would be to get the whole Groups-Table (and possibly more tables, if they are affected by the query) and perform the query on the client, which is of course undesirable. I guess the L2S designers decided that it would be counterintuitive if some queries took not-yet-committed inserts into account while others wouldn't, so they chose to never take them into account.
Why don't you use something like
foreach (var name in names.Distinct(StringComparer.InvariantCultureIgnoreCase))
to filter out duplicate names before hitting the database?
Why dont you try something like this
foreach (var name in names)
{
string s = name;
if (dataContext.Users.SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
{
dataContext.Users.InsertOnSubmit(new User { Name = name });
break;
}
}
I am sorry, I don't understand LINQ to SQL as much.
But, when I look at the code, it seems you are telling it to insert all the records at once (similar to a transaction) using SubmitChanges and you are trying to check the existence of it from the DB, when the records are not inserted at all.
EDIT: Try putting the SubmitChanges inside the loop and see that the code will run as per your expectation.
You can query the appropriate ChangeSet collection, such as
if(
dataContext.Users.
Union(dataContext.GetChangeSet().Inserts).
Except(dataContext.GetChangeSet().Deletes).
SingleOrDefault(u => u.Name.ToUpper() == s.ToUpper()) == null)
This will create a union of the values in the Users table and the pending Inserts, and will exclude pending deletes.
Of course, you might want to create a changeSet variable to prevent multiple calls to the GetChangeSet function, and you may need to appropriately cast the object in the collection to the appropriate type. In the Inserts and Deletes collections, you may want to filter it with something like
...GetChangeSet().Inserts.Where(o => o.GetType() == typeof(User)).OfType<User>()...
So, I'm trying to return a collection of People whose ID is contained within a locally created collection of ids ( IQueryable)
When I specify "locally created collection", I mean that the Ids collection hasnt come from a LinqToSql query and has been programatically created (based upon user input).
My query looks like this:
var qry = from p in DBContext.People
where Ids.Contains(p.ID)
select p.ID;
This causes the following exception...
"queries with local collections are not supported"
How can I find all the People with an id that is contained within my locally created Ids collection?
Is it possible using LinqToSql?
If Ids is a List, array or similar, L2S will translate into a contains.
If Ids is a IQueryable, just turn it into a list before using it in the query. E.g.:
List<int> listOfIDs = IDs.ToList();
var query =
from st in dc.SomeTable
where listOfIDs.Contains(st.ID)
select .....
I was struggling with this problem also. Solved my problem with using Any() instead
people.Where(x => ids.Any(id => id == x.ID))
As the guys mentioned above, converting the ids, which is of type IQueryable to List or Array will solve the issue, this will be translated to "IN" operator in SQL.But be careful because if the count of ids >= 2100 this will cause another issue which is "The server supports a maximum of 2100 parameters" and that is the maximum number of parameters(values) you can pass to "IN" in SQL server.
Another alternative would be keeping ids as IQueryable and using LINQ "Any" operator instead of "Contains", this will be translated to "EXISTS" in SQL server.
I'm sorry but the answers here didn't work for me as I'm doing dynamic types further along.
What I did was to use "UNION" in a loop which works great. Here's how:
var firstID = cityList.First().id;
var cities = dc.zs_Cities.Where(c => c.id == firstID);
foreach(var c in cityList)
{
var tempCity = c;
cities = cities.Union(dc.zs_Cities.Where(cty => cty.id == tempCity.id));
}