So I have a model created in Entity Framework 4 using the CTP4 code first features. This is all working well together.
I am attempting to add an advanced search feature to my application. This "advanced search" feature simply allows the users to enter multiple criteria to search by. For example:
Advanced Product Search
Name
Start Date
End Date
This would allow the user to search by the product name and also limit the results by the dates that they were created.
The problem is that I do not know how many of these fields will be used in any single search. How then can my Entity Framework query be constructed?
I have an example describing how to create a dynamic query for Entity Framework, however this does not seem to work for the POCO classes I created for Code First persistence.
What is the best way for to construct a query when the number of constraints are unknown?
So after some hours of work on this problem (and some help from our friend Google) I have found a workable solution to my problem. I created the following Linq expression extension:
using System;
using System.Linq;
using System.Linq.Expressions;
namespace MyCompany.MyApplication
{
public static class LinqExtensions
{
public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate)
{
if (condition)
return source.Where(predicate);
else
return source;
}
}
}
This extension allows for a Linq query to be created like this:
var products = context.Products.WhereIf(!String.IsNullOrEmpty(name), p => p.Name == name)
.WhereIf(startDate != null, p => p.CreatedDate >= startDate)
.WhereIf(endDate != null, p => p.CreatedDate <= endDate);
This allows each WhereIf statement to only affect the results if it meets the provided condition. The solution seems to work, but I'm always open to new ideas and/or constructive criticism.
John,
Your solution is absolutely awesome! But, just to share, I have been using this method above until I see your ideia.
var items = context.Items.Where(t => t.Title.Contains(keyword) && !String.IsNullOrEmpty(keyword));
So, it seems not to be the best solution for this, but for sure it is a way around.
Related
I was having some performance issues using SharpRepository, and after playing around the SQL Query Profiler I found the reason.
With EF I can do stuff like this:
var books = db.Books.Where(item => item.Year == '2016');
if (!string.IsNullorEmpty(search_author))
books = books.Where(item => item.Author.Contains(search_author);
return (books.ToList());
EF will not really do anything until books is used (last line) and then it will compile a query that will select only the small set of data matching year and author from the db.
But SharpRepository evaluates books at once, so this:
var books = book_repo.Books.FindAll(item => item.Year == '2016');
if (!string.IsNullorEmpty(search_author))
books = books.Where(item => item.Author.Contains(search_author);
return (books.ToList());
will compile a query like "select * from Books where Year == '2016'" at the first line, and get ALL those records from the database! Then at the second line it will make a search for the author within the C# code... That behaviour can be a major difference in performance when using large databases, and it explains why my queries timed out...
I tried using repo.GetAll().Where() instead of repo.FindAll().... but it worked the same way.
Am I misunderstanding something here, and is there a way around this issue?
You can use repo.AsQueryable() but by doing that you lose some of the functionality that SharpRepository can provide, like caching or and aspects/hooks you are using. It basically takes you out of the generic repo layer and lets you use the underlying LINQ provider. It has it's benefits for sure but in your case you can just build the Predicate conditionally and pass that in to the FindAll method.
You can do this by building an Expression predicate or using Specifications. Working with the Linq expressions does not always feel clean, but you can do it. Or you can use the Specification pattern built into SharpRepository.
ISpecification<Book> spec = new Specification<Book>(x => x.Year == 2016);
if (!string.IsNullorEmpty(search_author))
{
spec = spec.And(x => x.Author.Contains(search_author));
}
return repo.FindAll(spec);
For more info on Specifications you can look here: https://github.com/SharpRepository/SharpRepository/blob/develop/SharpRepository.Samples/HowToUseSpecifications.cs
Ivan Stoev provided this answer:
"The problem is that most of the repository methods return IEnumerable. Try repo.AsQueryable(). "
I want to include child objects on an IQueryable list..
I want to include a child object on selected columns of some table type IQueryable list..
I tried like this:
IQueryable<Persons> persons = Context.Persons.Select(x=> new persons{Pkid=x.pkid, FirstName=x.FirstName}).AsQueryable();
persons= persons.Include("Address");
this include of child objects is not working..anyone please help...where I am doing wrong..
thanks alot...
Include doesn't work with projection. Moreover it is not needed. Just do this:
var query = context.Persons
.Select(x => new PersonDto
{
Id = x.pkid,
FirstName = x.FirstName,
Address = x.Address
});
Few points here:
No Include
Address accessed directly in projection, EF will handle this
I'm using PersonDto as target of projection. PersonDto has just Id, FirstName and Address.
You can project to custom type or anonymous type but you cannot project to entity type (the mapped type) - it doesn't work and it throws exception.
If you want to use mapped type you can't return only selected scalar columns - all columns will always be loaded. Only navigation properties can be loaded selectively. To overcome this people sometimes use Table splitting but that is something which works if you can divide your big entity into disjunct entities. In your scenario use just projection.
You cannot use Include() on a projection, try this:
Iquerable<Persons> persons = Context.Persons
.Include("Address")
.Select(x=> new persons{Pkid=x.pkid, FirstName=x.FirstName})
.AsQuerable();
Also you have a naming conflict, you project to a type persons and want to hold the results in an IQueryable named persons - one of them is wrong. Is there a reason you need the projection at all? You could just do
Iquerable<Persons> persons = Context.Persons.Include("Address");
First: Check if lazy loading is enabled or not. I experienced different results when it was enabled. I prefer lazy loading being disabled.
Second: Check this syntax:
result = (From person In context.Persons.Include("Address")).ToList();
P.S.: Useful EF Tips & Tricks : http://blogs.msdn.com/b/alexj/archive/2009/03/26/index-of-tips.aspx
UPDATE:
Include is not working, because your are using it on newly created objects, not the objects available in the context. you should use Include before creating new objects.
Check This:
result = (From person In context.Persons.Include("Address") Select New With {.FirstName = item.FirstName, .AddressValue = item.Address.Value}).ToList();
I am writing a RIA service, which is also exposed using SOAP.
One of its methods needs to read data from a very big table.
At the beginning I was doing something like:
public IQueryable<MyItem> GetMyItems()
{
return this.ObjectContext.MyItems.Where(x => x.StartDate >= start && x.EndDate <= end);
}
But then I stopped because I was worried about the performance.
As far as I understand MyItemsis fully loaded and "Where" just filters the elements that were loaded at the first access of the property MyItems. Because MyItemswill have really lots of rows, I don't think this is the right approach.
I tried to google a bit the question but no interesting results came up.
So, I was thinking I could create a new instance of the context inside the GetMyItems method and load MyItems selectively. Something like:
public IQueryable<MyItems> GetMyItems(string Username, DateTime Start, DateTime End)
{
using (MyEntities ctx = new MyEntities ())
{
var objQuery = ctx.CreateQuery<MyItems>(
"SELECT * FROM MyItems WHERE Username = #Username AND Timestamp >= #Start AND Timestamp <= #End",
new ObjectParameter("#Username", Username),
new ObjectParameter("#Start", Start),
new ObjectParameter("#End", End));
return objQuery.AsQueryable();
}
}
But I am not sure at all this is the correct way to do it.
Could you please assist me and point out the right approach to do this?
Thanks in advance,
Cheers,
Gianluca.
As far as I understand MyItemsis fully loaded and "Where" just filters the elements that were loaded at the first access of the property MyItems.
No. That's entirely wrong. Don't fix "performance problems" until you actually have them. The code you already have is likely to perform better than the code you propose replacing it with. It certainly won't behave in the way you describe. But don't take my word for it. Use the performance profiler. Use SQL Profiler. And test!
I have a very small entity framework setup containing only a few related classes/tables and a view. I need to be able to pull a specific record from this view, namely, I need to be able to grab the record that meets two criteria, it has a specific ProfileID and a specific QuoteID.
This line is what's causing the problem:
TWProfileUpchargeTotal upchargeTotals = _context.TWProfileUpchargeTotals.Where(p => p.Profileid == profile.id && p.quoteid == _quote.quoteid).First();
I'm looping through the profiles I know about and getting their information from the view, so profile.id changes each time.
The first time this code executes it gets the correct record from the view.
The second and third (and presumably beyond that) time it executes, it retrieves the exact same record.
Any idea why or what I'm doing wrong here?
Thanks, in advance.
You've been bitten by the LINQ "gotcha" called closure. The following post (and many others) on SO detail this:
closure
What you need to do is declare a variable WITHIN the foreach you've ommited from the above code and assign the profile.id to this and use this in the Where clause.
foreach(Profile profile in ListOfProfiles)
{
var localProfile = profile;
TWProfileUpchargeTotal upchargeTotals = _context.TWProfileUpchargeTotals.Where(p => p.Profileid == localProfile.id && p.quoteid == _quote.quoteid).First();
}
I'm using Symfony 1.2 with Doctrine. I have a Place model with translations in two languages. This Place model has also a nested set behaviour.
I'm having problems now creating a new place that belongs to another node. I've tried two options but both of them fail:
1 option
$this->mergeForm(new PlaceTranslationForm($this->object->Translation[$lang->getCurrentCulture()]));
If I merge the form, what happens is that the value of the place_id field id an array. I suppose is because it is waiting a real object with an id. If I try to set place_id='' there is another error.
2 option
$this->mergeI18n(array($lang->getCurrentCulture()));
public function mergeI18n($cultures, $decorator = null)
{
if (!$this->isI18n())
{
throw new sfException(sprintf('The model "%s" is not internationalized.', $this->getModelName()));
}
$class = $this->getI18nFormClass();
foreach ($cultures as $culture)
{
$i18nObject = $this->object->Translation[$culture];
$i18n = new $class($i18nObject);
unset($i18n['id']);
$i18n->widgetSchema['lang'] = new sfWidgetFormInputHidden();
$this->mergeForm($i18n); // pass $culture too
}
}
Now the error is:
Couldn't hydrate. Found non-unique key mapping named 'lang'.
Looking at the sql, the id is not defined; so it can't be a duplicate record (I have a unique key (id, lang))
Any idea of what can be happening?
thanks!
It looks like the issues you are having are related to embedding forms within each other, which can be tricky. You will likely need to do things in the updateObject/bind methods of the parent form to get it to pass its values correctly to its child forms.
This article is worth a read:
http://www.blogs.uni-osnabrueck.de/rotapken/2009/03/13/symfony-merge-embedded-form/comment-page-1/
It gives some good info on how embedding (and mergeing) forms work. The technique the article uses will probably work for you, but I've not used I18n in sf before, so it may well be that there is a more elegant solution built in?