Mapping Read-only Entities

Artículo
11/08/2007

I can't take credit for the description of how to do this, but a very useful example was recently posted to the forum, and I wanted to make sure more people saw this/it is easy to find in the future. Also, Julie Lerman was mentioning to me today that there's a lot of good content in the forums which isn't as accessible as it should be so we ought to post more of these kinds of things to the blogs--feedback I intend to take to heart. So, here's the first installment on that new strategy:

From Srikanth Mandadi:

Mapping Read-only Entities

One of the options is to specify the mapping using QueryView elements in MSL file. Using this feature, you can describe the mapping for an EntitySet in Edm space using an Entity Sql query. The designer does not support this feature. So you might have to hand write the schema files.

Using QueryView elements currently has some restrictions:

If you specify a mapping for an EntitySet using a QueryView, you would have to map all the connected EntitySets and AssociationSets in the sub-graph using a QueryView.
You can not use all operators in Query Views. Some of the operators you can use are : Project, Join, Union, Case etc.

Here's a simple set of schemas that shows how to use this feature. These should work with Northwind DB. MSL file which is at the end is the most interesting for this scenario.

CSDL

<?xml version="1.0" encoding="utf-8"?>

<Summary>Summary: Entity Container for storing Northwind instances</Summary>

<LongDescription>LongDescription: This Entity Container is for storing Northwind instances</LongDescription>

</Documentation>

<Summary>EntitySet Products is for storing instances of EntityType Product</Summary>

<LongDescription>This EntitySet having name Products is for storing instances of EntityType Product</LongDescription>

</Documentation>

</EntitySet>

<Summary>EntitySet Categories is for storing instances of EntityType Category</Summary>

</Documentation>

</EntitySet>

<Summary>AssociationSet CategoryProducts is for storing instances of Association CategoryProduct</Summary>

<LongDescription>This AssociationSet having name=CategoryProducts is for storing instances of Association CategoryProduct</LongDescription>

</Documentation>

<Summary>This end of the relaitonship-instance describes the Category role for AssociationSet CategoryProducts</Summary>

</Documentation>

</End>

<LongDescription>This end of the relaitonship-instance describes the Product role for AssociationSet CategoryProducts</LongDescription>

</Documentation>

</End>

</AssociationSet>

</EntityContainer>

<Summary>Summary: EntityType named Product describes the content model for Product</Summary>

<LongDescription>LongDescription: The EntityType named Product describes the content model for Product</LongDescription>

</Documentation>

<Key>

</Key>

<Summary>Summary: This is the key property of EntityType Product</Summary>

<LongDescription>LongDescription: This is the key property of EntityType Product</LongDescription>

</Documentation>

</Property>

<Summary>Summary: This property describes the name of the Product</Summary>

</Documentation>

</Property>

<LongDescription>LongDescription: This property describes the quantity per unit corresponding to a product</LongDescription>

</Documentation>

</Property>

<Summary>This navigation property allows for traversing to Product-instances associated with a Category-instance</Summary>

</Documentation>

</NavigationProperty>

</EntityType>

<LongDescription>LongDescription: The EntityType named Category describes the content model for Category</LongDescription>

</Documentation>

<Key>

</Key>

</EntityType>

<Summary>Summary: EntityType named DiscontinuedProduct describes the content model for Product</Summary>

</Documentation>

</EntityType>

<Summary>Association CategoryProduct describes the participating end of the CategoryProduct relationship</Summary>

</Documentation>

<Summary>This end of the relationship-instance describes the Category role for Association CategoryProduct</Summary>

</Documentation>

</End>

<LongDescription>This end of the relationship-instance describes the Product role for Association CategoryProduct</LongDescription>

</Documentation>

</End>

</Association>

</Schema>

SSDL File :

<?xml version="1.0" encoding="utf-8"?>

<Summary>Entity Container for storing dbo instances</Summary>

<LongDescription>This Entity Container is for storing dbo instances</LongDescription>

</Documentation>

<Summary>EntitySet Products is for storing instances of EntityType Product</Summary>

<LongDescription>This EntitySet having name Products is for storing instances of EntityType Product</LongDescription>

</Documentation>

</EntitySet>

</AssociationSet>

</EntityContainer>

<Summary>EntityType named Product describes the content model for Product</Summary>

<LongDescription>The EntityType named Product describes the content model for Product</LongDescription>

</Documentation>

<Key>

</Key>

</EntityType>

<Key>

</Key>

</EntityType>

</Principal>

</Dependent>

</ReferentialConstraint>

</Association>

<Summary>This function accepts a source string, the starting position and the length of the sub-string to be extracted</Summary>

<LongDescription>This is a long Description. This function accepts a source string, the starting position and the length of the sub-string to be extracted</LongDescription>

</Documentation>

<Summary>The starting position of the substring</Summary>

<LongDescription>This is a long Description. The starting position of the substring</LongDescription>

</Documentation>

</Parameter>

</Function>

</Schema>

MSL File :

<?xml version="1.0" encoding="utf-8"?>

<Mapping xmlns="urn:

schemas-microsoft-com:windows:

storage:mapping:CS" Space="C-S">

SELECT VALUE Microsoft.CDP.Samples.Northwind.Category(C.CategoryID, C.CategoryName, C.Description)

FROM dbo.Categories as C

</QueryView>

</EntitySetMapping>

SELECT VALUE

CASE

WHEN P.Discontinued = False THEN Microsoft.CDP.Samples.Northwind.Product(P.ProductID, P.ProductName, P.QuantityPerUnit, P.UnitPrice, P.UnitsInStock, P.UnitsOnOrder, P.ReorderLevel)

ELSE Microsoft.CDP.Samples.Northwind.DiscontinuedProduct(P.ProductID, P.ProductName, P.QuantityPerUnit, P.UnitPrice, P.UnitsInStock, P.UnitsOnOrder, P.ReorderLevel)

END

FROM dbo.Products AS P WHERE P.Discontinued IN {True, False}

</QueryView>

SELECT VALUE

Microsoft.CDP.Samples.Northwind.Product(P.ProductID, "FooProduct", P.QuantityPerUnit, P.UnitPrice, P.UnitsInStock, P.UnitsOnOrder, P.ReorderLevel)

FROM dbo.Products AS P WHERE P.Discontinued = False

</QueryView>

</EntitySetMapping>

SELECT VALUE Microsoft.CDP.Samples.Northwind.CategoryProduct(CP.CategoryRef, CP.ProductRef)

FROM (

SELECT

CreateRef(Microsoft_CDP_Samples_Northwind_NorthwindContainer.Categories,

row(P.CategoryID),Microsoft.CDP.Samples.Northwind.Category) AS CategoryRef,

CreateRef(Microsoft_CDP_Samples_Northwind_NorthwindContainer.Products,

row(P.ProductID),Microsoft.CDP.Samples.Northwind.Product) AS ProductRef

FROM dbo.Products AS P) AS CP

</QueryView>

</AssociationSetMapping>

</EntityContainerMapping>

</Mapping>

Comments

Anonymous
November 07, 2007
PingBack from http://msdnrss.thecoderblogs.com/2007/11/08/mapping-read-only-entities/
Anonymous
November 07, 2007
Entity Framework FAQ Version 0.1 – first draft Contents 1. Introduction . 3 1.1. Why use EDM? How does
Anonymous
November 07, 2007
Version 0.1 – first draft, November 8, 2007 Contents 1. Introduction 1.1. About this FAQ… 1.2. Where
Anonymous
May 06, 2008
In Part 0: Introduction of this series after asking the question "Does the Entity Framework replace
Anonymous
June 11, 2008
The Entity Framework enables developers to reason about and write queries in terms of the EDM model rather than the logical schema of tables, joins, foreign keys, and so on. Many enterprise systems have multiple applications/databases with varying degrees
Anonymous
August 09, 2008
Part of the Entity Framework FAQ . 13. EDM 13.1. Does Entity Framework support Abstract types in EDM

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Mapping Read-only Entities

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