How do you include just a single entity per "main" entity in a query where the navigational property is a collection?
await _database.Table1
.AsQueryable()
.Include(t1 => t1.Table2.Where(t2 => t2.Id == t1.SingleTable2Id))
.FirstOrDefaultAsync();
The above doesn't seem to work. I get the following exception:
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'. See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.
Try this:
IQueryable query= _dbcontext.Table1
.AsQueryable();
As Queryable creates an expression tree that is not evaluated until fetch
you can add where expressions to your tree dynamically and assess include tables automatically.
Product[] products =
{
new Product {ProductId=1, Name="Kayak",Category="Watersports",Price=275m, Company=new Company{ CompanyName="Abc Corp",States=new String[]{"Ut","Id" } } },
new Product {ProductId=2, Name="Lifejacket", Category="Watersports",Price=48.95m, Company=new Company{ CompanyName="X Corp",States=new String[]{"Ca","Az" } }},
new Product {ProductId=3, Name="Soccer Ball", Category="Soccer",Price=19.50m, Company=new Company{ CompanyName="Y Corp",States=new String[]{"Tx","Wa" } }},
new Product {ProductId=4, Name="Corner Flag", Category="Soccer",Price=34.95m, Company=new Company{ CompanyName="Z Corp",States=new String[]{"Co","Wy" } }}
};
IQueryable<Product> query = products.
Where(e => e.Name == "Kayak")
.AsQueryable<Product>();
Product item = query.FirstOrDefault<Product>();
_output.WriteLine($"Item Name: {item.Name} Company: {item.Company.CompanyName}");
Related
I want to update the itemsToUpdate collection.
This collection is already used in a query thus the resulting entities are already tracked in the context local property.
What is the most efficient way of overriding properties of the context.items.Local property from the itemsToUpdate collection?
private async Task<IEnumerable<item>> GetitemsAsync(IEnumerable<item> itemIds)
{
return await context.items.Where(t => itemIds.Select(x => x.Id).Contains(t.Id)).ToListAsync();
}
public async Task Update(...)
{
// Update
var queryUpdateitems = await GetitemsAsync(itemsToUpdate);
bool canUpdate = queryUpdateitems.All(t => t.UserId == userId);
if (!canUpdate)
{
throw new NotAuthorizedException();
}
else
{
// update here the itemsToUpdate collection
}
context.SaveChangesAsync();
}
In your case, you know that you have to update all these items, you just want to make sure that current user can update all items (by comparing Item.UserId). Instead of fetching all the existing items from database to make the check, you can query database to give result of the check and then you can just send update to database if check is true.
var itemIds = itemsToUpdate.Select(x => x.Id).ToList();
var canUpdate = await db.Blogs.Where(b => itemIds.Contains(b.Id)).AllAsync(t => t.UserId == userId);
if (canUpdate)
{
db.UpdateRange(itemsToUpdate);
}
else
{
throw new NotSupportedException();
}
await db.SaveChangesAsync();
Here, you have to make list of itemIds first because EF cannot inline list of items in a query and will do evaluation on client otherwise. That means EF is fetching whole table. Same is true for your GetitemsAsync method. It also queries whole table. Consider creating itemIds locally in that method too.
Once you pass in List<int> in the method EF will be happy to inline it in query and for query of canUpdate it will sent single query to database and fetch just true/false from database. Then you can use UpdateRange directly since there are nomore tracking records. Since it does not fetch all items from database, it will be faster too.
I have three tables:
categories
id, title
products
id, name
categories_products
id, category_id, product_id
I have also setup the according models and relationships (both have belongsToMany of the other)
Now I want to get all products belonging to a category
Category::where('title','Electronics')->first()->products()->limit(10)->get(['products.name']);
which works fine, but I also want to include the category title for each product as well:
Category::where('title','Electronics')->first()->products()->limit(10)->get(['products.name','category.title']);
However it returns: Column not found category.title
I thought that the relation would take care of it.
EDIT: Models -->
Category:
class Category extends Model
{
protected $fillable = array('title');
public function products()
{
return $this->belongsToMany('Product', 'categories_products', 'category_id', 'product_id');
}
}
class Product extends Model
{
protected $fillable = array('name');
public function categories()
{
return $this->belongsToMany('Category', 'categories_products', 'product_id', 'category_id');
}
}
The reason you're getting the error is because get() works just like select() and because you're running the category query and then running the product query after there is no categories table to reference for the select.
Look into Eager Loading. It will help with a lot of these kinds of issues. Your query can be written as:
Product::select('id', 'name')
->with(['categories' => function($query) {
return $query->select('id', 'title');
}])
->whereHas('categories', function($query) {
return $query->where('title', 'Electronics');
})
->limit(10)
->get();
Because we are lazy loading you NEED the id column on each model so Laravel knows where to attach the relationships after the queries are run.
The with() method above will eager load the categories relationship and the whereHas() method puts a relationship constraint on the current query.
UPDATE
Similar query from Category model:
$category = Category::where('title','Electronics')
->with(['products' => function($query) {
return $query->select('id', 'name')->limit(10);
}])
->first(['id', 'title']);
Then access the products with:
$category->products
I'm developing a client app that uses breezejs and Entity Framework 6 on the back end. I've got a statement like this:
var country = 'Mexico';
var customers = EntityQuery.from('customers')
.where('country', '==', country)
.expand('order')
I want to use There may be hundreds of orders that each customer has made. For the purposes of performance, I only want to retrieve the latest order for each customer. This will be based on the created date for the order. In SQL, I could write something like this:
SELECT c.customerId, companyName, ContactName, City, Country, max(o.OrderDate) as LatestOrder FROM Customers c
inner join Orders o on c.CustomerID = o.CustomerID
group by c.customerId, companyName, ContactName, City, Country
If this was run against the northwind database, only the most recent order row is returned for each customer.
How can I write a similar query in breeze, so that it runs on the server side and therefore returns less data to the client. I know I could handle this all on the client but writing some javascript in a querysucceeded method that could be run by the client - but that's not the goal here.
thanks
For a case like this, you should create a special endpoint method that will perform your query.
Then you can use an Entity Framework query to do what you want, using the LINQ syntax.
Here are two Web API examples:
[HttpGet]
public IQueryable<Object> CustomersLatestOrderEntities()
{
// IQueryable<Object> containing Customer and Order entity
var entities = ContextProvider.Context.Customers.Select(c => new { Customer = c, LatestOrder = c.Orders.OrderByDescending(o => o.OrderDate).FirstOrDefault() });
return entities;
}
[HttpGet]
public IQueryable<Object> CustomersLatestOrderProjections()
{
// IQueryable<Object> containing Customer and Order entity
var entities = ContextProvider.Context.Customers.Select(c => new { Customer = c, LatestOrder = c.Orders.OrderByDescending(o => o.OrderDate).FirstOrDefault() });
// IQueryable<Object> containing just data fields, no entities
var projections = entities.Select(e => new { e.Customer.CustomerID, e.Customer.ContactName, e.LatestOrder.OrderDate });
return projections;
}
Note that you have a choice here. You can return actual entities, or you can return just some data fields. Which is right for you depends upon how you are going to use them on the client. If they are just for display in a
non-editable list, you can just return the plain data (CustomersLatestOrderProjections above). If they can potentially
be edited, then return the object containing the entities (CustomersLatestOrderEntities). Breeze will merge the entities
into its cache, even though they are contained inside this anonymous object.
Either way, because it returns IQueryable, you can use the Breeze filtering syntax from the client to further qualify the query.
var projectionQuery = breeze.EntityQuery.from("CustomersLatestOrderProjections")
.skip(20)
.take(10);
var entityQuery = breeze.EntityQuery.from("CustomersLatestOrderEntities")
.where('customer.countryName', 'startsWith', 'C');
.take(10);
I have an extension method defined like so:
public static TSource MaxBy<TSource, TResult>(this IEnumerable<TSource> collection, Func<TSource, TResult> func) where TSource : class
{
var comparer = Comparer<TSource>.Default;
TSource maxItem = null;
foreach (var item in collection)
{
if (comparer.Compare(item, maxItem) > 0)
maxItem = item;
}
return maxItem;
}
which I then use in the following LINQ-to-Entities query:
var balancesQuery = from t in db.Transactions
where t.UserId == userId
group t by t.CurrencyCode into tg
let tMaxDate = tg.MaxBy(i => i.TsCreate)
join c in db.Currencies on tg.Key equals c.CurrencyCode
select new { Currency = c, Balance = tMaxDate.Balance }
So what I'm doing is - get the newest transaction (MaxBy TsCreate) in each currency (group by CurrencyCode) and then select the balance against each of those transactions.
My problem is - this does not work with Entity Framework (LINQ-to-Entities; I get:
LINQ to Entities does not recognize the method 'Transaction MaxBy[Transaction,DateTime](System.Collections.Generic.IEnumerable'[Transaction], System.Func'2[Transaction,System.DateTime])' method, and this method cannot be translated into a store expression.
The same query works with LINQ to SQL.
My questions are:
Is there a way to make it work with Entity Framework?
Or maybe there is a better way of querying for the same information, which would work with Entity Framework?
Thanks in advance for any help!
Isn't the query same as:
var balancesQuery = from t in db.Transactions
where t.UserId == userId
group t by t.CurrencyCode into tg
join c in db.Currencies on tg.Key equals c.CurrencyCode
select new {
Currency = c,
Balance = tg.OrderByDescending(i => i.TsCreate).Take(1).Balance
};
You can't use extensions with LINQ queries that actually pull data from the database as it's impossible for this to be turned into SQL. However, you can do this by returning the results into memory using ToArray() or ToList() to trigger the database query executing and then call your extension functions on resultant real data in memory.
I have a default Entity Framework model that holds all of my default tables for my product, and that all customers share in common. However, on some customers, I have some custom tables that exist for only that customer, but they relate to the default product's tables. I have a second Entity Framework model to hold these custom tables.
My question is how can I make a Linq to Entities query using Join so I can relate the entities from my default model to the tables on my custom model? I don't mind not having the Navigation properties from the custom entity to the entities on the default model; I just need a way to query both models in a single query.
Below is the code:
using (ProductEntities oProductDB = new ProductEntities())
{
using (ProductEntitiesCustom oProductCustomDB = new ProductEntitiesCustom())
{
var oConsulta = oProductCustomDB.CTBLCustoms
.Where(CTBLCustoms => CTBLCustoms.IDWOHD >= 12)
.Join(oProductDB.TBLResources,
CTBLCustoms => new
{
CTBLCustoms.IDResource
},
TBLResources => new
{
TBLResources.IDResource
},
(CTBLCustoms, TBLResources) => new
{
IDCustom = CTBLCustoms.IDCustom,
Descricao = CTBLCustoms.Descricao,
IDWOHD = CTBLCustoms.IDWOHD,
IDResource = CTBLCustoms.IDResource,
ResourceCode = TBLResources.Code
});
gvwDados.DataSource = oConsulta;
}
}
I get a The specified LINQ expression contains references to queries that are associated with different contexts error.
EDIT
Could I merge the 2 ObjectContext into a third, and then run the Linq query?
Tks
EDIT
Below is the code that worked, using the AsEnumerable() proposed solution:
using (ProductEntities oProductDB = new ProductEntities())
{
using (ProductEntitiesCustom oProductCustomDB = new ProductEntitiesCustom())
{
var oConsulta = (oProductCustomDB.CTBLCustoms.AsEnumerable()
.Where(CTBLCustoms => CTBLCustoms.IDWOHD >= 12)
.Join(oProductDB.TBLResources,
CTBLCustoms => new
{
CTBLCustoms.IDResource
},
TBLResources => new
{
TBLResources.IDResource
},
(CTBLCustoms, TBLResources) => new
{
IDCustom = CTBLCustoms.IDCustom,
Descricao = CTBLCustoms.Descricao,
IDWOHD = CTBLCustoms.IDWOHD,
IDResource = CTBLCustoms.IDResource,
ResourceCode = TBLResources.Code
})).ToList();
gvwDados.DataSource = oConsulta;
}
}
I added the AsEnumerable() as suggested, but I had to add the ToList() at the end so I could databind it to the DataGridView.
You can't do this in L2E. You could bring this into object space with AsEnumerable(), and it would work, but possibly be inefficient.
Merging the ObjectContexts is possible, and would work, but would need to be done manually.