Edition 0 Updated to asp. Net core 0

public
abstract
class
BaseSpecification : ISpecification 
{ 
public
BaseSpecification
(Expressionbool
>> criteria) 
{ 
Criteria = criteria; 
} 
public
Expressionbool
>> Criteria { 
get
; } 
public
Listobject
>>> Includes { 
get
; } = 
new
Listobject
>>>(); 
public
List<
string
> IncludeStrings { 
get
; } = 
new
List<
string
>(); 
protected
virtual
void
AddInclude
(Expressionobject
>> includeExpression) 
{ 
Includes.
Add
(includeExpression); 
} 
// string-based includes allow for including children of children
// e.g. Basket.Items.Product
protected
virtual
void
AddInclude
(
string
includeString) 
{ 
IncludeStrings.
Add
(includeString); 
} 
} 

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CHAPTER 6 | Tackle Business Complexity in a Microservice with DDD and CQRS Patterns 
The following specification loads a single basket entity given either the basket’s ID or the ID of the 
buyer to whom the basket belongs. It will 
eagerly load
 
the basket’s 
Items
collection. 
// SAMPLE QUERY SPECIFICATION IMPLEMENTATION
public
class
BasketWithItemsSpecification : BaseSpecification 
{ 
public
BasketWithItemsSpecification
(
int
basketId) 
: 
base
(b => b.
Id
== basketId) 
{ 
AddInclude
(b => b.
Items
); 
} 
public
BasketWithItemsSpecification
(
string
buyerId) 
: 
base
(b => b.
BuyerId
== buyerId) 
{ 
AddInclude
(b => b.
Items
); 
} 
} 
And finally, you can see below how a generic EF Repository can use such a specification to filter and 
eager-load data related to a given entity type T. 
// GENERIC EF REPOSITORY WITH SPECIFICATION
// https://github.com/dotnet-architecture/eShopOnWeb
public
IEnumerable 
List
(ISpecification spec) 
{ 
// fetch a Queryable that includes all expression-based includes
var
queryableResultWithIncludes = spec.
Includes
.
Aggregate
(_dbContext.
Set
().
AsQueryable
(), 
(current, include) => current.
Include
(include)); 
// modify the IQueryable to include any string-based include statements
var
secondaryResult = spec.
IncludeStrings
.
Aggregate
(queryableResultWithIncludes, 
(current, include) => current.
Include
(include)); 
// return the result of the query using the specification's criteria expression
return
secondaryResult 
.
Where
(spec.
Criteria
) 
.
AsEnumerable
(); 
} 
In addition to encapsulating filtering logic, the specification can specify the shape of the data to be 
returned, including which properties to populate. 
Although we don’t recommend returning 
IQueryable
from a repository, it’s perfectly fine to use them 
within the repository to build up a set of results. You can see this approach used in the List method 
above, which uses intermediate 
IQueryable
expressions to build up the query’s list of includes before 
executing the query with the specification’s criteria 
on the last line. 
Learn 
how the specification pattern is applied in the eShopOnWeb sample
. 

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CHAPTER 6 | Tackle Business Complexity in a Microservice with DDD and CQRS Patterns