ObjectQueryTObject Class

Represent LINQ query, which queries the domain objects repository

Inheritance Hierarchy

SystemObject
  Aloe.SystemFrameworks.Domain.LINQObjectQueryTObject
    Aloe.SystemFrameworks.Domain.LINQDataAccessObjectQueryTObject
    Aloe.SystemFrameworks.Domain.LINQVirtualObjectQueryTObject

Namespace: Aloe.SystemFrameworks.Domain.LINQ
Assembly: Aloe.SystemFrameworks.Domain (in Aloe.SystemFrameworks.Domain.dll) Version: 20.1.3.5

Syntax

C++

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public abstract class ObjectQuery<TObject> : IOrderedQueryable<TObject>, 
	IEnumerable<TObject>, IEnumerable, IOrderedQueryable, IQueryable, IQueryable<TObject>, 
	IQueryProvider
where TObject : DomainObject

Public MustInherit Class ObjectQuery(Of TObject As DomainObject)
	Implements IOrderedQueryable(Of TObject), IEnumerable(Of TObject), 
	IEnumerable, IOrderedQueryable, IQueryable, IQueryable(Of TObject), 
	IQueryProvider

generic<typename TObject>
where TObject : DomainObject
public ref class ObjectQuery abstract : IOrderedQueryable<TObject>, 
	IEnumerable<TObject>, IEnumerable, IOrderedQueryable, IQueryable, IQueryable<TObject>, 
	IQueryProvider

[<AbstractClassAttribute>]
type ObjectQuery<'TObject when 'TObject : DomainObject> =  
    class
        interface IOrderedQueryable<'TObject>
        interface IEnumerable<'TObject>
        interface IEnumerable
        interface IOrderedQueryable
        interface IQueryable
        interface IQueryable<'TObject>
        interface IQueryProvider
    end

Type Parameters

TObject: The domain object which is queried

The ObjectQueryTObject type exposes the following members.

Constructors

	Name	Description
	ObjectQueryTObject	Creates new instance, with the default expression

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Properties

	Name	Description
	ElementType	Gets the type of the element(s) that are returned when the expression tree associated with this instance of IQueryable is executed.
	Expression	Gets the expression tree that is associated with the instance of IQueryable.
	Provider	Gets the query provider that is associated with this data source.
	Repository	The repository, which is queried by this query
	Transaction	The transaction to which this query is bound

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Methods

	Name	Description
	CreateQuery(Expression)	Constructs an IQueryable object that can evaluate the query represented by a specified expression tree.
	CreateQueryTElement(Expression)	Constructs an IQueryableT object that can evaluate the query represented by a specified expression tree.
	Execute(Expression)
	ExecuteTResult(Expression)	Executes the specified expression.
	GetEnumerator	Returns an enumerator that iterates through the collection.
	ReadCount	Executes the query and returns the result records count.
	ReadToBuffer	Executes the query and returns the result in a buffer.

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Extension Methods

	Name	Description
	PreloadTObject(ILazyProperty)	Overloaded. Preloads the value of the specified lazy property for the objects in the sequence. (Defined by LinqExtensions.)
	PreloadTObject, TResult(ExpressionFuncTObject, TResult)	Overloaded. Preloads the full object state for all objects returned by applying the expression to each element in source. This is still a research method, which will be renamed later to .Preload(). (Defined by LinqExtensions.)
	SplitTObject	Splits the input IEnumerable in chunks with the specified size. (Defined by Splitter.)
	TopologicalSortTObject	Topological sort based on item dependencies. (Defined by RepositoryExtensions.)

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Remarks

The ObjectQuery is used to form and execute LINQ queries against object repositories. It contains translator, that supports a subset of the full LINQ command set. The following constructs are supported:

SELECT

Only full object selects are supported, no projections. Example:

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from cust in transaction.Query<Customer>()
where ...
select cust;

However, projections are supported after enumeration, as in the following example (pay attention to the .ToList() method call):

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from cust in Transaction.Query<Customer>().ToList()
select new { cust.Id, cust.Number };

Take()

Take() is equivalent to SQL's TOP clause and limits the rows returned by the query to the specified number. Example:

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var query =
  (from cust in transaction.Query<Customer>()
  where ...
  select cust).Take(10);

This will generate SQL similar to:

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SELECT TOP 10 * FROM Customers WHERE ...

WHERE

1. Normal comparison expression

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from cust in transaction.Query<Customer>()
where cust.CustomerNumber == "A1035"
select cust;

This will generate SQL similar to:

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SELECT * FROM Customers WHERE CustomerNumber = "A1035"

2. Boolean comparison

Boolean fields do not need comparison operator. Example:

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from cust in transaction.Query<Customer>()
where cust.IsActive
select cust;

This will generate SQL similar to:

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SELECT * FROM Customers WHERE IsActive = 1

3. Including NULLs

You can include null values for fields using the following syntax:

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from cust in transaction.Query<Customer>()
where (cust.FromDate ?? DateTime.MinDate) < someDate
select cust;

This will generate SQL similar to:

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SELECT * FROM Customers WHERE FromDate < someDate OR FromDate IS NULL

4. In

4.1. You can match a field to a list of values using the following syntax:

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var guids = new List<int>() { 1, 2, 3 };
var query = 
  from cust in transaction.Query<Customer>()
  where cust.Id.In(guids)
  select cust;

//this will translate to the same as above, but is more unnatural
var query = 
  from cust in transaction.Query<Customer>()
  where guids.Contains(cust.Id)
  select cust;

Both constructs will generate SQL similar to:

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SELECT * FROM Customers WHERE CustomerId IN (1,2,3)

4.2. For references, you can also use .In. For example:

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//make a list of Customer objects
var customers = new List<Customer>() { 
  transaction.Get<Customer>(Guid.Parse("00f6eb9e-74fe-e111-82b1-00155d001f00")),
  transaction.Get<Customer>(Guid.Parse("e12d956b-2c8d-463a-bb9f-fa8f2dd6d3c8")),
  transaction.Get<Customer>(Guid.Parse("00f6eb9e-74fe-e111-82b1-00155d001f00")),
  };
//use the list to get all invoices of the three customers  
var query = 
  from inv in transaction.Query<Invoice>()
  where inv.Customer.In(customers)
  select cust;

4.3. You can even use another query variable as list provider or directly nest a query

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var customers = transaction.Query<Customer>().Take(3);

var query = 
  from inv in transaction.Query<Invoice>()
  where inv.Customer.In(customers)
  select inv;

var query = 
  from inv in transaction.Query<Invoice>()
  where inv.Customer.In(
    transaction.Query<Customer>().Take(3)
    )
  select inv;

5. .Like()

.Like() can be used for pattern based matching similar to SQL's LIKE operator. Example:

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var query = 
  from cust in transaction.Query<Customer>()
  where cust.CustomerNumber.Like("%106%")
  select cust;

This will generate SQL similar to:

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SELECT * FROM Customers WHERE CustomerNumber LIKE '%106%'

6. Filtering by parent table

You can filter by the attributes of a parent table. Please, keep in mind, that this does not work for ALL references, but only for ownership references. Examples:

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//this will return all products in groups, whose name contains 'tes'
var query =
  from p in transaction.Query<Product>()
  where p.ProductGroup.Name.Like("%tes%")
  select p;

//select all lines, belonging to sales orders, whose date is after 2013/1/1
var query2 =
  from l in transaction.Query<SalesOrderLine>()
  where l.SalesOrder.DocumentDate >= new DateTime(2013, 1, 1)
  select l;

//this will throw exception, because ProductType is not the owner of Product
var query3 = 
  from p in transaction.Query<Product>()
  where p.ProductType.Name.Like("%tes%")
  select p;

The first two queries will generate SQL similar to:

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SELECT P.*
FROM Products P 
     JOIN ProductGroups PG 
     ON PG.Id = P.ProductGroupId
WHERE PG.Name LIKE '%tes%'

SELECT SOL.*
FROM SalesOrderLines SOL
     JOIN SalesOrders SO
     ON SO.Id = SOL.SalesOrderId
     JOIN Documents D
     ON D.Id = SO.DocumentId
WHERE D.DocumentDate >= '20130101'

Reference

Aloe.SystemFrameworks.Domain.LINQ Namespace

ObjectQueryAddLanguageSpecificTextSet("LSTB263C5CD_0?cs=&lt;|vb=(Of |cpp=&lt;|fs=&lt;'|nu=(");TObjectAddLanguageSpecificTextSet("LSTB263C5CD_1?cs=&gt;|vb=)|cpp=&gt;|fs=&gt;|nu=)"); Class

Type Parameters

Reference

ObjectQueryTObject Class