I've the following Entity Model : Employee has a Company and a Company has Employees.
When using the Include statement like below:
var query = context.Employees.Include(e => e.Company);
query.Dump();
All related data is retrieved from the database correctly. (Using LEFT OUTER JOIN on Company table)
The problem is hat when I use the GroupBy() from System.Linq.Dynamic to group by Company.Name, the Employees are missing the Company data because the Include is lost.
Example:
var groupByQuery = query.GroupBy("new (Company.Name as CompanyName)", "it");
groupByQuery.Dump();
Is there a way to easily retrieve the applied Includes on the 'query' as a string collection, so that I can include them in the dynamic GroupBy like this:
var groupByQuery2 = query.GroupBy("new (Company, Company.Name as CompanyName)", "it");
groupByQuery2.Dump();
I thought about using the ToString() functionality to get the SQL Command like this:
string sql = query.ToString();
And then use RegEx to extract all LEFT OUTER JOINS, but probably there is a better solution ?
if you're creating the query in the first place - I'd always opt to save the includes (and add to them if you're making a composite query/filtering).
e.g. instead of returning just 'query' return new QueryContext {Query = query, Includes = ...}
I'd like to see a more elegant solution - but I think that's your best bet.
Otherwise you're looking at expression trees, visitors and all those nice things.
SQL parsing isn't that straight either - as queries are not always that simple (often a combo of things etc.).
e.g. there is a `span' inside the query object (if you traverse a bit) which seems to be holding the 'Includes' but it's not much help.
Related
There is a table, it is a poco entity generated by entity framework.
class Log
{
int DoneByEmpId;
string DoneByEmpName
}
I am retrieving a list from the data base. I want distinct values based on donebyempid and order by those values empname.
I have tried lot of ways to do it but it is not working
var lstLogUsers = (context.Logs.GroupBy(logList => logList.DoneByEmpId).Select(item => item.First())).ToList(); // it gives error
this one get all the user.
var lstLogUsers = context.Logs.ToList().OrderBy(logList => logList.DoneByEmpName).Distinct();
Can any one suggest how to achieve this.
Can I just point out that you probably have a problem with your data model here? I would imagine you should just have DoneByEmpId here, and a separate table Employee which has EmpId and Name.
I think this is why you are needing to use Distinct/GroupBy (which doesn't really work for this scenario, as you are finding).
I'm not near a compiler, so i can't test it, but...
Use the other version of Distinct(), the one that takes an IEqualityComparer<TSource> argument, and then use OrderBy().
See here for example.
Ok I have seen many questions that based on their text could be something like this but not quite. Say I have something like this
(from r in reports
join u in SECSqlClient.DataContext.GetTable<UserEntity>()
on r.StateUpdateReportUserID equals u.lngUserID
select r).
If reports have a bunch of say reportDTO class and I want to select from a list of that DTO but at the same time set one property to a property in userEntity how would I do that? Basically I want all other fields on the report maintained but set a user name from the user table. (There is a reason this is not done in one big query that gets a list of reports)
What I am looking for is something like Select r).Something(SOME LAMBDA TO SET ONE FIELD TO userEntity property).
There is a dirty way to do this, which is
var repQuery = from r in reports ... select new { r, u };
var reps = repQuery.Select(x => { x.r.Property1 = x.u.Property1; return x.r; };
However, When it comes to functional programming (which Linq is, arguably) I like to adhere to its principles, one of which to prevent side effects in functions. A side effect is a change in state outside the function body, in this case the property value.
On the other hand, this is a valid requirement, so I would either use the ForEach method after converting the query to list (ToList()). Foreach is expected to incur side effects. Or I would write a clearly named extension method on IEnumerable<T> (e.g. DoForAll) that does the same, but in a deferred way. See Why there is no ForEach extension method on IEnumerable?.
I have an application that manages documents called Notes. Like a blog, Notes can be searched for matches against one or more Tags, which are contained in a Note.Tags collection property. A Tag has Name and ID properties, and matches are made against the ID. A user can specify multiple tags to match against, in which case a Note must contain all Tags specified to match.
I have a very complex LINQ query to perform a Note search, with extension methods and looping. Quite frankly, it has a real code smell to it. I want to rewrite the query with something much simpler. I know that if I made the Tag a simple string, I could use something like this:
var matchingNotes = from n in myNotes
where n.Tags.All(tag => searchTags.Contains(tag))
Can I do something that simple if my model uses a Tag object with an ID? What would the query look like. Could it be written in fluent syntax? what would that look like?
I believe you can find notes that have the relevant tags in a single LINQ expression:
IQueryable<Note> query = ... // top part of query
query = query.Where(note => searchTags.All(st =>
note.Tags.Any(notetag => notetag.Id == st.Id)));
Unfortunately there is no “fluent syntax” equivalent for All and Any, so the best you can do there is
query = from note in query
where searchTags.All(st =>
note.Tags.Any(notetag => notetag.Id == st.Id))
select note;
which is not that much better either.
For starters see my comment; I suspect the query is wrong anyway! I would simplifiy it, by simply enforcing separately that each tag exists:
IQueryable<Note> query = ... // top part of query
foreach(var tagId in searchTagIds) {
var tmpId = tagId; // modified closures...
query = query.Where(note => note.Tags.Any(t => t.Id == tmpId));
}
This should have the net effect of enforcing all the tags specified are present and accounted for.
Timwi's solution works in most dialects of LINQ, but not in Linq to Entities. I did find a single-statement LINQ query that works, courtesy of ReSharper. Basically, I wrote a foreach block to do the search, and ReSharper offered to convert the block to a LINQ statement--I had no idea it could do this.
I let ReSharper perform the conversion, and here is what it gave me:
return searchTags.Aggregate<Tag, IQueryable<Note>>(DataStore.ObjectContext.Notes, (current, tag) => current.Where(n => n.Tags.Any(t => t.Id == tag.Id)).OrderBy(n => n.Title));
I read my Notes collection from a database, using Entity Framework 4. DataStore is the custom class I use to manage my EF4 connection; it holds the EF4 ObjectContext as a property.
DynamicObject LINQ query with the List compiles fine:
List<string> list = new List<string>();
var query = (from dynamic d in list where d.FirstName == "John" select d);
With our own custom class that we use for the "usual" LINQ compiler reports the error "An expression tree may not contain a dynamic
operation":
DBclass db = new DBclass();
var query = (from dynamic d in db where d.FirstName == "John" select d);
What shall we add to handle DynamicObject LINQ?
Does DBClass implement IEnumerable? Perhaps there is a method on it you should be calling to return an IEnumerable collection?
You could add a type, against which to write the query.
I believe your problem is, that in the first expression, where you are using the List<>, everything is done in memory using IEnumerable & Link-to-Objects.
Apparently, your DBClass is an IQueryable using Linq-to-SQL. IQueryables use an expression tree to build an SQL statement to send to the database.
In other words, despite looking much alike, the two statements are doing radically different things, one of which is allowed & one which isn't. (Much in the way var y = x * 5; will either succeed or fail depending on if x is an int or a string).
Further, your first example may compile, but as far as I can tell, it will fail when you run it. That's not a particular good benchmark for success.
The only way I see this working is if the query using dynamic is made on IEnumerables using Link-to-Objects. (Load the full table into a List, and then query on the list)
Why do I get the error:
Unable to create a constant value of type 'Closure type'. Only
primitive types (for instance Int32, String and Guid) are supported in
this context.
When I try to enumerate the following Linq query?
IEnumerable<string> searchList = GetSearchList();
using (HREntities entities = new HREntities())
{
var myList = from person in entities.vSearchPeople
where upperSearchList.All( (person.FirstName + person.LastName) .Contains).ToList();
}
Update:
If I try the following just to try to isolate the problem, I get the same error:
where upperSearchList.All(arg => arg == arg)
So it looks like the problem is with the All method, right? Any suggestions?
It looks like you're trying to do the equivalent of a "WHERE...IN" condition. Check out How to write 'WHERE IN' style queries using LINQ to Entities for an example of how to do that type of query with LINQ to Entities.
Also, I think the error message is particularly unhelpful in this case because .Contains is not followed by parentheses, which causes the compiler to recognize the whole predicate as a lambda expression.
I've spent the last 6 months battling this limitation with EF 3.5 and while I'm not the smartest person in the world, I'm pretty sure I have something useful to offer on this topic.
The SQL generated by growing a 50 mile high tree of "OR style" expressions will result in a poor query execution plan. I'm dealing with a few million rows and the impact is substantial.
There is a little hack I found to do a SQL 'in' that helps if you are just looking for a bunch of entities by id:
private IEnumerable<Entity1> getByIds(IEnumerable<int> ids)
{
string idList = string.Join(",", ids.ToList().ConvertAll<string>(id => id.ToString()).ToArray());
return dbContext.Entity1.Where("it.pkIDColumn IN {" + idList + "}");
}
where pkIDColumn is your primary key id column name of your Entity1 table.
BUT KEEP READING!
This is fine, but it requires that I already have the ids of what I need to find. Sometimes I just want my expressions to reach into other relations and what I do have is criteria for those connected relations.
If I had more time I would try to represent this visually, but I don't so just study this sentence a moment: Consider a schema with a Person, GovernmentId, and GovernmentIdType tables. Andrew Tappert (Person) has two id cards (GovernmentId), one from Oregon (GovernmentIdType) and one from Washington (GovernmentIdType).
Now generate an edmx from it.
Now imagine you want to find all the people having a certain ID value, say 1234567.
This can be accomplished with a single database hit with this:
dbContext context = new dbContext();
string idValue = "1234567";
Expression<Func<Person,bool>> expr =
person => person.GovernmentID.Any(gid => gid.gi_value.Contains(idValue));
IEnumerable<Person> people = context.Person.AsQueryable().Where(expr);
Do you see the subquery here? The generated sql will use 'joins' instead of sub-queries, but the effect is the same. These days SQL server optimizes subqueries into joins under the covers anyway, but anyway...
The key to this working is the .Any inside the expression.
I have found the cause of the error (I am using Framework 4.5). The problem is, that EF a complex type, that is passed in the "Contains"-parameter, can not translate into an SQL query. EF can use in a SQL query only simple types such as int, string...
this.GetAll().Where(p => !assignedFunctions.Contains(p))
GetAll provides a list of objects with a complex type (for example: "Function"). So therefore, I would try here to receive an instance of this complex type in my SQL query, which naturally can not work!
If I can extract from my list, parameters which are suited to my search, I can use:
var idList = assignedFunctions.Select(f => f.FunctionId);
this.GetAll().Where(p => !idList.Contains(p.FunktionId))
Now EF no longer has the complex type "Function" to work, but eg with a simple type (long). And that works fine!
I got this error message when my array object used in the .All function is null
After I initialized the array object, (upperSearchList in your case), the error is gone
The error message was misleading in this case
where upperSearchList.All(arg => person.someproperty.StartsWith(arg)))