I have many to one relationship defined within my model:
Project.CreatedBy = ApplicationUser.Id:
class Project{
[Required]
public ApplicationUser CreatedBy {get; set;}
}
With mapping:
modelBuilder.Entity<Project>().HasOptional(i => i.CreatedBy).WithOptionalDependent().WillCascadeOnDelete(false);
Unfortunatelly, when I try to retrieve all users from DbContext by:
var users = context.Users;
Generated SQL looks like:
SELECT
[...]
FROM [dbo].[AspNetUsers] AS [Extent1]
LEFT OUTER JOIN [dbo].[Projects] AS [Extent4] ON ([Extent4].[CreatedBy_Id] IS NOT NULL) AND ([Extent1].[Id] = [Extent4].[CreatedBy_Id])
So when certain user have created 10 projects, the user entity is multiplied 10 times. It makes me impossible to look for that user by his username:
context.Users.Single(u => u.Username == "test")
because it would give me Sequence contains more than one element exception.
Do you have any idea how to avoid that extra join?
I suspect it has something to do with modelBuilder declaration. I've been googling about this, but never found any solution.
Any materials about modelBuilder and defining relationships with it would be really appreciated too.
The mapping...
modelBuilder.Entity<Project>()
.HasOptional(i => i.CreatedBy)
.WithOptionalDependent()
...expresses this as a 1:1 association, not the 1:n association you intend it to be.
So change the mapping into one-to-many:
modelBuilder.Entity<Project>()
.HasOptional(p => p.CreatedBy)
.WithMany()
.HasForeignKey(p => p.CreatedBy_Id);
I'm not sure why EF joins in the Project when you query User because the association is optional), but a proper 1:n mapping will stop this.
Use
.FirstOrDefault()
instead of Single.
This method will return first object or null if object is not found. Single method throws exception if more than one element is selected.
You can also use
.First()
But this method will throw exception if no elements found.
PS I'm not sure if it's a typo, but you have to use double equal sign, like that:
context.Users.Single(u => u.Username == "test")
And keep in mind that usually in these cases LoweredUsername column is created and used for compare:
context.Users.Single(u => u.LoweredUsername == providedUsername.ToLower())
Reasons for that:
Someone can type John instead of john
Indexing on SQL server side works in this case
I suppose in ApplicationUser you have
public virtual ICollection<Project> Projects { get; set; }
Please see turn off lazy loading for all entities in MSDN
Or to turning off lazy loading for specific navigation properties make the Projects property non-virtual
Related
Here is my Enum:
public enum AdvertStatus
{
Active,
Archived
}
And my entity type:
public record Advertisement
{
...
public AdvertStatus Status { get; set; }
...
}
In database it's stored as int, Database is Postgree
When I try to compare it like so:
data = data.Where(x => x.Status == searchValues.Status);
Entity Framework throws an exception sayng:
.Status == (int)__searchValues_Status_3)' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to 'AsEnumerable', 'AsAsyncEnumerable', 'ToList', or 'ToListAsync'.
I tried solutions from this question: LINQ TO ENTITY cannot compare to enumeration types but it did't work.
EDIT 1:
data is database table context IQueryable<AdvertisementDTO>
searchValues.Status is type of AdvertStatus from search filter
The issue may be higher up in your Linq query, such as you are attempting to project with a Select or ProjectTo before filtering. For simple types like int/string this should work, but depending on how your DTO is declared you might be introducing problems for mpgsql.
For instance if your query is something like:
var query = _context.Advertisements
.Select(x => new AdvertisementDTO
{
// populate DTO
}).Where(x => x.Status == searchValues.Status)
// ....
then npgsql may be having issues attempting to resolve the types between what is in the DTO and the enumeration in your searchValues. From what the exception detail looks like, npgsql is trying to be "safe" with the enum and casting to intbut feeding that to PostgreSQL that results in invalid SQL. I did some quick checks and the DTO would need to be using the same Enum type (C# complains if the DTO cast the value to int, cannot use == between AdvertStatus and int fortunately) The project may have something like a value converter or other hook trying to translate enumerations which is getting brought into the mix and gunking up the works.
Try performing the Where conditions prior to projection:
var query = _context.Advertisements
.Where(x => x.Status == searchValues.Status)
.Select(x => new AdvertisementDTO
{
// populate DTO
})
// ....
If the data value is stored as an Int then this should work out of the box. npgsql does support mapping to string (which would require a ValueConverter) as well as database declared enumerations. (https://www.postgresql.org/docs/current/datatype-enum.html) However, Int columns should work fine /w enums.
If that doesn't work, I'd try with a new DbContext instance pointed at the DB and a simple entity with that Enum to load a row from that table to eliminate whether npgsql is translating the enum correctly, just to eliminate any possible converters or other code that the main DbContext/models/DTOs may be contributing.
It was all my mistake in higher repo Select projection.
Thanks you all for help. Cheers.
I have an entity called Comment, which has an enum property of type CommentType:
public class Comment
{
public virtual Guid Id { get; private set; }
public virtual CommentType CommentType { get; set; }
// other prop removed for simplicity
}
public enum CommentType
{
Comment,
Correction,
Improvement,
BugFix,
NewFeauture,
Other
}
I need to select the comments from database by the alphabetically value of the CommentType enum, something like
_db.Comments.OrderBy(p => p.CommentType)
However, the Enum values are treated as integers, and the sort will not work alphabetically correctly.
Is there any way to add some attributes / metadata to the Enum values to make them sort correctly alphabetically?
One solution will be to assign the integer value to enum values, but i already have many database records that will need to be updated. And this solution is not good for new added enum values.
public enum CommentType
{
Comment = 2,
Correction = 3,
Improvement = 4,
BugFix = 1,
NewFeauture = 5,
Other = 6
}
Currently your enum name is not known at database level so in my opinion you have two options.
Use value on server side:
_db.Comments.ToList().OrderBy(p => p.CommentType.ToString())
Add value on database side: You should create table that will contain comment type names. And then you can create foreign key between comments and commentTypeNames and use simple select:
_db.Comments.OrderBy(c => c.CommentTypeNames.Name)
or just make join:
_db.Comments
.Join(
_db.CommentTypeNames,
c => c.CommentType,
ctn => ctn.CommentType,
(c, ctn) => new { Comment = c, CommentName = ctn })
.OrderBy(g => g.CommentName.Name)
.Select(g => g.Comment);
There are also computed columns. I never used those though so I dont have experience. Maybe you could add column that will be resolved to string by CASE statements on database. However I am not sure how will this affect performance/maintainability. For more info you could check http://geekswithblogs.net/DavidPaquette/archive/2012/09/23/calculated-columns-in-entity-framework-code-first-migrations.aspx
For performance reasons I would advise to take option 2, it's better to do such things in database.
I assume that you are using code first so maybe this post will be helpful for you: EF5 Code First Enums and Lookup Tables
This idea of a table is nice of course, especially when the enum has many values and is likely to get new ones. However, when enum values are added both the code and the database need to be maintained.
In general when the enum is volatile I would not use an enum but only the table.
But when it is not likely to change much, you could also consider to stick with the enum simply write out the order instruction:
_db.Comments.OrderBy(p =>
p.CommentType == CommentType.Comment ? "Comment" :
p.CommentType == CommentType.Correction ? "Correction" :
p.CommentType == CommentType.Improvement? "Improvement" :
.... :
"ZZZ")
As an alternative you may convert CommentType property in your Comment class into foreign key 'CommentTypeId' pointing at CommentType(Id, Name) table, that has your Id values and corresponding text Name.
This will let you order by text easily.
Web services cannot return an anonymous type.
If you are building a LINQ query using classes through a datacontext... you cannot construct instances of those classes in a query.
Why would I want to do this? Say I want to join three "tables" or sets of objects. I have three items with a foreign key to each other. And say the lowest, most detailed of these was represented by a class that had fields from the other two to represent the data from those. In my LINQ query I would want to return a list of the lowest, most detailed class. This is one way I have decided to "join some tables together" and return data from each of them via LINQ to SQL via a WebService. This may be bad practice. I certainly do not like adding the additional properties to the lowest level class.
Consider something like this... (please ignore the naming conventions, they are driven by internal consideration) also for some reason I need to instantiate an anonymous type for the join... I don't know why that is... if I do not do it this way I get an error...
from su in _dataContext.GetTable<StateUpdate>()
join sfs in _dataContext.GetTable<SystemFacetState>()
on new { su.lngSystemFacetState } equals new { lngSystemFacetState = sfs.lngSystemFacetState }
join sf in _dataContext.GetTable<SystemFacet>()
on new { sfs.lngSystemFacet } equals new { lngSystemFacet = sf.lngSystemFacet }
join s in _dataContext.GetTable<System>()
on new { sf.lngSystem } equals new {lngSystem = s.lngSystem}
select new
{
lngStateUpdate = su.lngStateUpdate,
strSystemFacet = sf.strSystemFacet,
strSystemFacetState = sfs.strSystemFacetState,
dtmStateUpdate = su.dtmStateUpdate,
dtmEndTime = su.dtmEndTime,
lngDuration = su.lngDuration,
strSystem = s.strSystem
}
).ToList();
Notice I have to build the anonymous type which is composed of pieces of each type. Then I have to do something like this... (convert it to a known type for transport via the web service)
result = new List<StateUpdate>(from a in qr select(new StateUpdate
{
lngStateUpdate = a.lngStateUpdate,
strSystemFacet = a.strSystemFacet,
strSystemFacetState = a.strSystemFacetState,
dtmStateUpdate = a.dtmStateUpdate,
dtmEndTime = a.dtmEndTime,
lngDuration = a.lngDuration,
strSystem = a.strSystem
}));
It is just awful. And perhaps I have created an awful mess. If I am way way off track here please guide me to the light. I feel I am missing something fundamental here when I am adding all these "unmapped" properties to the StateUpdate class.
I hope someone can see what I am doing here so I can get a better way to do it.
You can create a 'dto' class which just contains the properties you need to return and populate it instead of the anonymous object:
public class Result
{
public string lngStateUpdate
{
get;
set;
}
... // other properties
}
then use it like this:
from su in _dataContext.GetTable<StateUpdate>()
...
select new Result
{
lngStateUpdate = su.lngStateUpdate,
... // other properties
}
Nitpick note - please ditch the Hungarian notation and camel casing for properties :)
I think the answer is to create another object to serve as a DTO. This object would not be mapped to the data context and can contain fields that cross the mapped objects. This solves the problems of repetitive properties in the mapped objects, and allows for instantiation of the DTO class in the query as it is not mapped.
FYI: with respect to the problem with the join- I revisited that and I think I may have had the inner and outer components of the join switched around before.
I recently started working with ServiceStack and its ORMLite framework. I have searched on Google and browsed the source code but couldn't find anything relevent.
Is there any way to select specific columns when executing a query with ORMLite ?
Something like that : Db.First<Model>(q => q.Id == someId, "Column1, Column2")
Unless I missed this feature, I am surprised nobody asked about this before, since this is one the rule of thumbs to optimize your DB transactions.
If you want to specify columns other that the table you need to use SQL as seen in this earlier example
So in your case you could do something like:
Db.First<Model>("SELECT Column1, Column2 FROM AnyTableOrView");
You can also create a partial model that looks at your table by decorating it with the [Alias] attribute, like:
[Alias("AnyTableOrView")]
public class Model {
public int Id { get; set; }
public string Column1 { get; set; }
public string Column2 { get; set; }
}
Then you can do something like:
Db.First<Model>(q => q.Id == someId);
And it will only SELECT + populate fields from the partial model.
I did try this :
Created a Database VIEW (table name and columns are already set)
Created a class named "Event" and matching each fields for that table with a property
(i used [Alias] for table name and for all columns to have nice names)
Wrote access to DB to select 1 record based on it's ID
var dbFactory = new OrmLiteConnectionFactory(
"Data Source=MyDB;User Id=user;Password=pwd", // Connection String
OracleDialect.Provider);
using (var db = dbFactory.OpenDbConnection())
{
var event = db.GetByIdOrDefault<Event>( request.Id );
}
At that point the var 'event' is populated but only the Id field is filled !
all the others fields of the class are not filled (while there are really data in database).
It's the simplest i can do and it does not work. Any ideas ?
(PS : i am using OrmLite for Oracle)
Thanks
I have found the problem.
It was due to an incorrect type matching between field in my class (defined as a string) and the corresponding Oracle Field (that is a DATE).
I replaced the string with datetime and worked like a charm.
So it's working perfectly with a VIEW and that's GREATLY simplify the code.
I had a similar problem, however my solution was different.
I had a int property in my POCO. My query (from Oracle) was returning a null for this property. It caused a exception to be raised and prevented further processing of that row.
The result was a partial populated POCO.
The solution was to change to type to be nullable.
public int? mypropperty
My scenario:
This is an ASP.NET 4.0 web app programmed via C#
I implement a repository pattern. My repositorys all share the same ObjectContext, which is stored in httpContext.Items. Each repository creates a new ObjectSet of type E. Heres some code from my repository:
public class Repository<E> : IRepository<E>, IDisposable
where E : class
{
private DataModelContainer _context = ContextHelper<DataModelContainer>.GetCurrentContext();
private IObjectSet<E> _objectSet;
private IObjectSet<E> objectSet
{
get
{
if (_objectSet == null)
{
_objectSet = this._context.CreateObjectSet<E>();
}
return _objectSet;
}
}
public IQueryable<E> GetQuery()
{
return objectSet;
}
Lets say I have 2 repositorys, 1 for states and 1 for countrys and want to create a linq query against both. Note that I use POCO classes with the entity framework. State and Country are 2 of these POCO classes.
Repository stateRepo = new Repository<State>();
Repository countryRepo = new Repository<Country>();
IEnumerable<State> states = (from s in _stateRepo.GetQuery()
join c in _countryRepo.GetQuery() on s.countryID equals c.countryID
select s).ToList();
Debug.WriteLine(states.First().Country.country)
essentially, I want to retrieve the state and the related country entity. The query only returns the state data... and I get a null argument exception on the Debug.WriteLine
LazyLoading is disabled in my .edmx... thats the way I want it.
You're doing a join without retrieving anything from it. There are multiple solutions to your problem:
Use Include to load the dependent entities: from s in ((ObjectSet<State>) _stateRepo.GetQuery).Include("Country"). The problem with this approach is that you should expose the ObjectSet directly rather than as a IQueryable if you want to avoid casting.
Use context.LoadProperty(states.First(), s => s.Country) to explicitly load the Country from the database for a given state.
Select both entities in the query: from s in ... join c ... select new { s, c }. You won't be able to access directly the state's Country property but you have it in the anonymous type.
Enable lazy loading.
Your repository implementation is very similar to mine, especially the way you are storing the ObjectContext. It works fine for me, so I don't think it's a conceptual problem.
Try using a static objectcontext (no wrapper) just to see if that fixes the problem. Perhaps there is a bug in your ContextHelper which causes your context to get disposed and recreated.