I have a the following query but showing error. how can GroupBy ?
IList<tbl_roadmapautomation> allproductdata = _context.tbl_roadmapautomation.GroupBy(p=>p.Stream).ToList();
Here "Stream" is a column name which i want to GroupBy.
ERROR: Cannot implicitly convert type 'System.Collections.Generic.List>' to 'System.Collections.Generic.IList'.
An explicit conversion exists (are you missing a cast?)
Please suggest me how can solve this error.Advance thanks for the help.
var allproductdata =
_context.tbl_roadmapautomation.GroupBy(p=>p.Stream).ToList();
will work
You need convert from this result to an IList<> (eg, with a cast).
But I don't think you want to -- IList is just the interface definition, why would you want a list like that?
Using var is nice when used inside a method, but what if you need to assign the data to a property that is needed for binding purposes. In this case,
public class RoadMapViewModel
{
IList<IGrouping<int, tbl_roadmapautomation>> allproductdata {get; set;}
// constructor
public RoadMapViewModel(){
allproductdata = _context.tbl_roadmapautomation.GroupBy(p=>p.Stream).ToList();
}
}
Related
I have a pretty simple setyp where I'm putting graphql over an entityframework datacontext (sql server).
I'm trying to get filtering to work. I've tried adding .UseFiltering() to a field descriptor like so...
descriptor.Field(t => t.AccountName).Type<NonNullType<StringType>>().UseFiltering();
But it causes this error on startup...
HotChocolate.SchemaException: 'Unable to infer or resolve a schema
type from the type reference Input: System.Char.'
I assume I'm doing something wrong somewhere...
"UseFiltering" is supposed to be used to filter data which represents a collection of items in some way (IQueryable, IEnumerable, etc).
For instance, if you have users collection and each user has AccountName property you could filter that collection by AccountName:
[ExtendObjectType(Name = "Query")]
public class UserQuery
{
[UseFiltering]
public async Task<IEnumerable<User>> GetUsers([Service]usersRepo)
{
IQueryable<User> users = usersRepo.GetUsersQueryable();
}
}
In that example the HotChocolate implementation of filtering will generate a number of filters by user fields which you can use in the following way:
users(where: {AND: [{accountName_starts_with: "Tech"}, {accountName_not_ends_with: "Test"}]})
According to your example: the system thinks that AccountName is a collection, so tries to build filtering across the chars the AccountName consists of.
I have the following container :
BeanContainer<Integer, Person> container = new BeanContainer<Integer, Person>(Person.class);
container.setBeanIdProperty("lastName");
Where person has a "lastName", "firstName" and "town" attributes.
I'm passing this container to my table :
table.setContainerDataSource(container);
The problem is that I want to have a bean id property value (called "fullname") that is the result of the lastname and firstname concatenation.
How can I do this wit the setTableFieldFactory and createField methods ?
Thank you.
It seems that you need a simple autogenerated column. Here is a sample: http://dev.vaadin.com/svn/versions/6.1/src/com/vaadin/demo/featurebrowser/GeneratedColumnExample.java
One way of doing it is to add a getter method getFullName() to your Person class which concatanes and than returns the name+surname fields
fmucar is right.
do not forget to include a setter too.
In some case a Property.ReadOnlyException will be throw if you miss to include a setter.
If you can do not use GeneratedColum because of the folowing point :
the visible display will be regenerated at any interaction (to try this you can add a generated column who return a random number).
the container know only the visible part. So sorting could be tricky.
I have a database that has a user search screen that is "dynamic" in that I can add additional search criteria on the fly based on what columns are available in the particular view the search is based on and it will allow the user to use them immediately. Previously I had been using nettiers for this database, but now I am programming a new application against it using RIA and EntFramework 4 and LINQ.
I currently have 2 tables that are used for this, one that fills the combobox with the available search string patterns:
LastName
LastName, FirstName
Phone
etc....
then I have an other table that splits those criteria out and is used in my nettiers algorithms. It works well, but I want to use LINQ..and it doesnt fit this model very well. Besides I think I can pare it down to just one table with linq...
using a format similar to this or something very close...
ID Criteria WhereClause
1 LastName 'Lastname Like '%{0}%'
now I know this wont fit specifically into a linq query..but I am trying to use a univeral syntax for clarity here...
the real where clause would look something like this: a=>a.LastName.Contains("{0}")
My first question is: Is that even possible to do? Feed a lambda in to a string and use it in a Linq Query?
My second question is: at one point when I was researching this before I found a linq syntax that had a prefix like it.LastName{0}
and I appear to have tried using it because vestiges of it are still in my test databases...but I dont know recall where I read about it.
Is anyone doing this? I have done some searches and found similar occurances but they mostly have static fields that are optional, not exactly the way I am doing it...
As for your first question, you can do this using Dynamic Linq as described by Scott Gu here
var query = Northwind.Products.Where("Lastname LIKE "test%");
I'm not sure how detailed your dynamic query needs to be, but when I need to do dynamic queries, I create a class to represent filter values. Then I pass that class to a search method on my repository. If the value for a field is null then the query ignores it. If it has a value it adds the appropriate filter.
public class CustomerSearchCriteria{
public string LastName { get; set; }
public string FirstName { get; set; }
public string PhoneName { get; set; }
}
public IEnumberable<Customer> Search(CustomerSearchCriteria criteria){
var q = db.Customers();
if(criteria.FirstName != null){
q = q.Where(c=>c.FirstName.Contains(criteria.FirstName));
}
if(criteria.LastName!= null){
q = q.Where(c=>c.LastName.Contains(criteria.LastName));
}
if(criteria.Phone!= null){
q = q.Where(c=>c.Phone.Contains(criteria.Phone));
}
return q.AsEnumerable();
}
We are building dynamic search expressions using the Dynamic Linq library. We have run into an issue with how to construct a lamba expression using the dynamic linq library for navigation properties that have a one to many relationship.
We have the following that we are using with a contains statement-
Person.Names.Select(FamilyName).FirstOrDefault()
It works but there are two problems.
It of course only selects the FirstOrDefault() name. We want it to use all the names for each person.
If there are no names for a person the Select throws an exception.
It is not that difficult with a regular query because we can do two from statements, but the lambda expression is more challenging.
Any recommendations would be appreciated.
EDIT-
Additional code information...a non dynamic linq expression would look something like this.
var results = persons.Where(p => p.Names.Select(n => n.FamilyName).FirstOrDefault().Contains("Smith")).ToList();
and the class looks like the following-
public class Person
{
public bool IsActive { get; set;}
public virtual ICollection<Name> Names {get; set;}
}
public class Name
{
public string GivenName { get; set; }
public string FamilyName { get; set; }
public virtual Person Person { get; set;}
}
We hashed it out and made it, but it was quite challenging. Below are the various methods on how we progressed to the final result. Now we just have to rethink how our SearchExpression class is built...but that is another story.
1. Equivalent Query Syntax
var results = from person in persons
from name in person.names
where name.FamilyName.Contains("Smith")
select person;
2. Equivalent Lambda Syntax
var results = persons.SelectMany(person => person.Names)
.Where(name => name.FamilyName.Contains("Smith"))
.Select(personName => personName.Person);
3. Equivalent Lambda Syntax with Dynamic Linq
var results = persons.AsQueryable().SelectMany("Names")
.Where("FamilyName.Contains(#0)", "Smith")
.Select("Person");
Notes - You will have to add a Contains method to the Dynamic Linq library.
EDIT - Alternatively use just a select...much more simple...but it require the Contains method addition as noted above.
var results = persons.AsQueryable().Where("Names.Select(FamilyName)
.Contains(#0", "Smith)
We originally tried this, but ran into the dreaded 'No applicable aggregate method Contains exists.' error. I a round about way we resolved the problem when trying to get the SelectMany working...therefore just went back to the Select method.
I have an entity and its mapping:
public class Test
{
public virtual int Id { get; set; }
public virtual string Name { get; set; }
public virtual string Description { get; set; }
}
public class TestMap : EntityMap<Test>
{
public TestMap()
{
Id(x => x.Id);
Map(x => x.Name);
Map(x => x.Description);
}
}
I'm trying to run a query on it (to grab it out of the database):
var keyword = "test" // this is coming in from the user
keyword = keyword.ToLower(); // convert it to all lower-case
var results = session.Linq<Test>
.Where(x => x.Name.ToLower().Contains(keyword));
results.Count(); // execute the query
However, whenever I run this query, I get the following exception:
Index was out of range. Must be non-negative and less than the size of the
collection. Parameter name: index
Am I right when I say that, currently, Linq to NHibernate does not support ToLower()? And if so, is there an alternative that allows me to search for a string in the middle of another string that Linq to NHibernate is compatible with? For example, if the user searches for kap, I need it to match Kapiolani, Makapuu, and Lapkap.
I had this happen recently. I can tell you that ToLower() does not work and that Contains() and StartsWith() do work and are not case sensitive. You can get the desired affect by using Contains() and StartsWith() directly.
There seems to be a lot of confusion around this subject.
The "old" Linq provider (for NHibernate 2.x) probably might not support this. If that's the case, it never will because it's not maintained anymore.
The new provider (included with NHibernate 3.x) does support it (although ToUpper and ToLower seem to be inverted, see http://groups.google.com/group/nhibernate-development/browse_thread/thread/a167216e466b3241)
Contains and StartsWith map to the LIKE operator in SQL. They are not case insensitive themselves; it's the collation that makes them case insensitive, so that depends on how your column/schema were created.
Update (2010-04-09): bug confirmed and patch submitted, see https://nhibernate.jira.com/browse/NH-2169
Update (2010-05-21): patch was applied on 2010-05-01 and works as expected now.
According to the comments in these two blog posts this functionality is not implemented yet.
You might want to confirm whether the database uses case sensitivity.
If it doesn't, then you don't need .ToLower()
The accepted answer mentions using Contains() and StartsWith() which are good. but wouldn't work in cases when you want to be sure both strings are the same.
Using "==" will suffice since it is also case-insensitive. So, you no longer need to use ToLower() nor ToUpper();