With a plain connection to SQL Server, you can specify what columns to return in a simple SELECT statement.
With EF:
Dim who = context.Doctors.Find(3) ' Primary key is an integer
The above returns all data that entity has... BUT... I would only like to do what you can with SQL and get only what I need.
Doing this:
Dim who= (From d In contect.Doctors
Where d.Regeneration = 3
Select New Doctor With {.Actor = d.Actor}).Single
Gives me this error:
The entity or complex type XXXXX cannot be constructed in a LINQ to Entities query.
So... How do I return only selected data from only one entity?
Basically, I'm not sure why, but Linq can't create the complex type. It would work if you were creating a anonymous type like (sorry c# code)
var who = (from x in contect.Doctors
where x.Regeneration == 3
select new { Actor = x.Actor }).Single();
you can then go
var doctor = new Doctor() {
Actor = who.Actor
};
but it can't build it as a strongly typed or complex type like you're trying to do with
var who = (from x in contect.Doctors
where x.Regeneration == 3
select new Doctor { Actor = x.Actor }).Single();
also you may want to be careful with the use of single, if there is no doctor with the regeneration number or there are more than one it will throw a exception, singleordefault is safer but it will throw a exception if there is more than one match. First or Firstordefault are much better options First will throw a exception only if none exist and Firstordefault can handle pretty much anything
The best way to do this is by setting the wanted properties in ViewModel "or DTO if you're dealing with upper levels"
Then as your example the ViewModel will be:
public class DoctorViewModel{
public string Actor {get;set;}
// You can add as many properties as you want
}
then the query will be:
var who = (From d In contect.Doctors
Where d.Regeneration = 3
Select New DoctorViewModel {Actor = d.Actor}).Single();
Sorry i wrote the code with C# but i think the idea is clear :)
You can just simply do this:
Dim who= (From d In contect.Doctors
Where d.Regeneration = 3
Select d.Actor).Single
Try this
Dim who = contect.Doctors.SingleOrDefault(Function(d) d.Regeneration = 3).Actor
Related
So am using AspNetCore 1.0 with EFCore 1.0, both latest releases as far as I am aware.
Executing a query to delete an object using the FromSql method on a DbSet throws an exception. Both the code and exception are below.
public void DeleteColumn(int p_ColumnID)
{
int temp = p_ColumnID;
string query = "DELETE FROM Columns WHERE ID = {0}";
var columnsList = m_context.Columns.FromSql(query, p_ColumnID).ToList();
foreach (Columns c in columnsList)
{
m_context.Columns.Remove(c);
}
m_context.SaveChanges();
}
After executing the FromSql call, I get the following exception
An exception of type 'System.NotSupportedException' occurred in Remotion.Linq.dll but was not handled in user code
Additional information: Could not parse expression 'value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[ASPNET5_Scrum_Tool.Models.Columns]).FromSql("DELETE FROM Columns WHERE ID = {0}", __p_0)': This overload of the method 'Microsoft.EntityFrameworkCore.RelationalQueryableExtensions.FromSql' is currently not supported.
I have no clue how to fix this error and from Googling I have come across no similar problems.
I am also wondering, if the query/code was successful it would return an 'IQueryable object. Would that solely contain the results of the query, in this case the specific Column object to delete?
FromSql is intended to allow you to compose a custom SQL SELECT statement that will return entities. Using it with a DELETE statement is not appropriate here, since your goal is to load the records you want to delete and then delete them using the default Entity Framework mechanism. A Delete statement generally does not return the records deleted (though there are ways to accomplish that). Even if they did, the records will already be deleted and so you won't want to iterate over them and do a Remove on them.
The most straightforward way to do what you want might be to use the RemoveRange method in combination with a Where query.
public void DeleteColumn(int p_ColumnID)
{
m_context.Columns.RemoveRange(m_context.Columns.Where(x => x.ID == p_ColumnID))
m_context.SaveChanges();
}
Alternately, if you want to load your entities and iterate manually through them to
public void DeleteColumn(int p_ColumnID)
{
columnList = m_context.Columns.Where(x => x.ID == p_ColumnID);
foreach (Columns c in columnsList)
{
m_context.Columns.Remove(c);
}
m_context.SaveChanges();
}
If you really want to issue the Delete statement manually, as suggested by Mike Brind, use an ExecuteSqlCommand method similar to:
public void DeleteColumn(int p_ColumnID)
{
string sqlStatement = "DELETE FROM Columns WHERE ID = {0}";
m_context.Database.ExecuteSqlCommand(sqlStatement, p_ColumnID);
}
I had the same exception in a case where I did not use delete statement. Turns out I was using the In-Memory Database. Since it is not a real database you can't use FromSQL.
I know this may sound nonsense but I will try my best to explain the problem that I am facing with neo4jClient.
I developing a Social TaskManagment Software. and for the server side code and data Storage I choose to have neo4j (neo4jClient) and C# in place.
in Our software Imagine a User : (mhs) Post a Task of "#somebody please help me on #Neo4j #cypher" the task would be decorated with some fancy character including (# # + /) the obove post will be save in neo4j as graph like this :
(post:Post {Text : #somebody please help me on #Neo4j})-[Has_HashTag]-(neo4j:HashTag)
(post:Post)-[Has_HashTag]-(Cypher: HashTag)
(post:Post)-[Has_Author)-[mhs:User]
(post:Post)-[Has_MentionedUser)-[Somebody:User]
Now Imagine User #mhs is trying to search the Post that Have HashTag of #Neo4j and mentioned to #somebody
Here I am building (hand Craft) a Cypher Query Including the 2 seach Paramerts in Cypher with Some Fancy C# code which result the blow Cypher Query:
MATCH (nodes)-[r]-(post:Post),
(post:Post)-[:HAS_MentionedUsers]->(assignee1307989068:User),
(nodes)-[r]-(post:Post)-[:HAS_HashTags]->(Hashtag1482870844:HashTag)
WHERE (assignee1307989068.UserName = "somebody") AND (Hashtag1482870844.Value = "neo4j")
RETURN post AS Post, Collect(nodes) as nodes
ORDER BY post.creationDate
the above cypher will return a post with just all the nodes of the post that is not included in Where clause.
my question is how to include all the Nodes related to the Targeted (post) without including them in Return part of the cypher. Something like return (*).
The Other problem is How can I deserialize the result set into C# without knowing what shape it may have.
The Search method that I am producing the mentioned Cypher is as fallow:
public List<PostNode> Search(string searchterm)
{
List<string> where = new List<string>();
var tokenizedstring = searchterm.Split(' ');
var querystring = new StringBuilder();
var relatedNodes = new List<string>();
var q = new CypherFluentQuery(_graphClient) as ICypherFluentQuery;
foreach (var t in tokenizedstring)
{
_commandService.BuildPostQueystring(t, ref querystring, ref where, ref relatedNodes);
}
if (querystring[querystring.Length - 1] == ',')
querystring = querystring.Remove(querystring.Length - 1, 1);
q = q.Match(querystring.ToString());
int i = 1;
if (where.Count > 0)
q = q.Where(where[0]);
while (i < where.Count)
{
q = q.AndWhere(where[i]);
i++;
}
var rq = q.Return(
(post, nodes) => new PostNode
{
Post = post.As<Node<string>>(),
Nodes = nodes.CollectAs<string>()
})
.OrderBy("post.creationDate");
var results = rq.Results.ToList();
//foreach (var result in results)
//{
// //dynamic p = JsonConvert.DeserializeObject<dynamic>(result.Post.Data);
// //dynamic d = JsonConvert.DeserializeObject<dynamic>(result.Nodes.Data);
//}
return results;
}
}
//Some Helper Class just to cast the result.
public class PostNode
{
public Node<string> Post { get; set; }
public IEnumerable<Node<string>> Nodes { get; set; }
}
But as you may noticed it does not have the nodes that is included in the search term via Where Clause in Cypher Query.
I am really stopped here for a while, as I can not provide any decent solution for this. so your help may save me a lot.
may be i am totally in a wrong direction so please help in any way you can think of.
It appears that a list of UNKNOWN related nodes are being provisioned, so one of this:
Scenario A
It doesn't matter what EXACTLY those related nodes are, I just want them.
Question: What is intention of retrieving those unknown but related nodes? By answering this chances are this query could be improved for good.
Scenario B
These unknown related nodes are actually known! It's just they are not fully known at time of query execution however down the road somewhere in C# code we will have things like this
if (nodes.Any(_ => _ is HashTag) {...}
Question:
This type of behaviour requires to KNOW the type. Even with reflection or C# dynamic stuff that requirement is still there because Neo4jClient has no way of correlating a bag of JSON data coming from Neo4j into any local type. When Neo4jClient receives bulk of data over wire somehow it should know what type would YOU prefer to represent. This is why queries are always like this:
Return((a, p) => new
{
Author = a.As<Author>(), //we expect node content to be represented as Author
Post = p.As<Post>()
})
Neo4jClient does NOT preserve C# types inside your Neo4j database. It would have been nasty to do so. However, idea behind it is that you shouldn't find yourself desperate for it and if you do so then I would recommend looking for problem somewhere else i.e. why would you rely on your client library to describe your domain for you?
I am struggling with linq to get the datetime.
I am trying to get the info if the records are less than the current date
Here is the code:
public ActionResult _Events()
{
DateTime dt = DateTime.Now.Date;
var DocsFirst =(from t in db.tble_presentation
where dt >= EntityFunctions.TruncateTime(t.presentation_date)
select t).OrderByDescending(t => t.presentation_date).Take(2);
return PartialView(new Newsmodel
{
DocsList_list1 = DocsFirst,
});
}
but I get this following error
Cannot implicitly convert type 'System.Linq.IQueryable' to
'System.Linq.IOrderedEnumerable'. An explicit conversion exists
(are you missing a cast?)
thanks in advance
Hesh
It looks like DocsList_List1 is of type IOrderedEnumerable (as #Emre points out in the comment). To make the code compile, you either have to change the declaration of DocsList_list1 to be of a compatible type (probably IEnumerable) or make the result of the linq query an IOrderedEnumerable. An (somewhat ugly) way to do the latter:
var DocsFirst = (from t in db.tble_presentation
where dt >= EntityFunctions.TruncateTime(t.presentation_date)
select t).Take(2).AsEnumerable()
.OrderByDescending(t => t.presentation_date);
It's somewhat ugly because it does the ordering in memory instead of letting the database do it, but it still only reads the two requested elements thanks to Take(2) being placed before AsEnumerable().
The problem:
Exception Details: System.InvalidOperationException: The model item
passed into the dictionary is of type
'System.Data.Entity.Infrastructure.DbQuery`1[System.Int32]', but this
dictionary requires a model item of type 'migros.Models.State'.
What I'm trying to do
I need to pass the result of the following linq query to a View.
using (var db = new migros_mockEntities1())
{
var listOfIdeas = (from x in db.States select x.ID);
return View(listOfIdeas);
}
The View requires IEnumerable, but it seems I can't cast the result of the linq query to IEnumerable.
I'm using entity framework database first approach.
The problem is that you trying to return ObjectQuery from within the using block.
Try to materialize your object-set
var listOfIdeas = (from x in db.States select x.ID).ToList();
Also, dont forget, that dealing with context can be tricky.
In your case var listOfIdeas = (from x in db.States select x.ID) is just a query, that will run only when you'd begin to iterate over it. So, if context gets already disposed you'd get an exception, trying to use listOfIdeas.
Is there any way to use DataContext to execute some explicit SQL and return the auto-increment primary key value of the inserted row without using ExecuteMethodCall? All I want to do is insert some data into a table and get back the newly created primary key but without using LINQ (I use explicit SQL in my queries, just using LINQ to model the data).
Cheers
EDIT: Basically, I want to do this:
public int CreateSomething(Something somethingToCreate)
{
string query = "MyFunkyQuery";
this.ExecuteCommand(query);
// return back the ID of the inserted value here!
}
SOLUTION
This one took a while. You have to pass a reference for the OUTPUT parameter in your sproc in your parameter list of the calling function like so:
[Parameter(Name = "InsertedContractID", DbType = "Int")] ref System.Nullable<int> insertedContractID
Then you have to do
insertedContractID = ((System.Nullable<int>)(result.GetParameterValue(16)));
once you've called it. Then you can use this outside of it:
public int? CreateContract(Contract contractToCreate)
{
System.Nullable<int> insertedContractID = null; ref insertedContractID);
return insertedContractID;
}
Take heavy note of GetParameterValue(16). It's indexed to whichever parameter it is in your parameter list (this isn't the full code, by the way).
You can use something like this:
int newID = myDataContext.ExecuteQuery<int>(
"INSERT INTO MyTable (Col1, Col2) VALUES ({0}, {1});
SELECT Convert(Int, ##IDENTITY)",
val1, val2).First();
The key is in converting ##IDENTITY in type int, like Ben sugested.
If you insist on using raw sql queries, then why not just use sprocs for your inserts? You could get the identity returned through an output parameters.
I'm not the greatest at SQL, but I broke out LinqPad and came up with this. It's a big hack in my opinion, but it works ... kinda.
DataContext.ExecuteQuery<T>() returns an IEnumerable<T> where T is a mapped linq entity. The extra select I added will only populate the YourPrimaryKey property.
public int CreateSomething(Something somethingToCreate)
{
// sub out your versions of YourLinqEntity & YourPrimaryKey
string query = "MyFunkyQuery" + "select Convert(Int, SCOPE_IDENTITY()) as [YourPrimaryKey]";
var result = this.ExecuteQuery<YourLinqEntity>(query);
return result.First().YourPrimaryKey;
}
You'll need to modify your insert statement to include a SELECT ##Identity (SQL Server) or similar at the end.