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.NET/ASP.NET/C#/VB.NET PDF Document SDKTo get consistent results you d want to make sure the initial query and subsequent lazy loads happen as part of a transaction (as shown later), but to ensure scalability in a busy system you want to minimize the number of requests made in any single transaction. So you can tell the EF that you want certain related entities to be fetched at the same time as the main result. You do this with the Include method shown in Example 14-8, which is available on any of the entity sets provided by the context. add qr code to ssrs report, ssrs upc-a, how to create barcodes in visual basic .net, ssrs ean 128, ssrs ean 13, ssrs pdf 417, itextsharp remove text from pdf c#, itextsharp replace text in pdf c#, ssrs data matrix, c# remove text from pdf,var customersWithOrderDetails = dbContext.Customers. Include("SalesOrderHeaders.SalesOrderDetails"); Customer myCustomer = customersWithOrderDetails.Single( cust => cust.CustomerID == 29531); Console.WriteLine(myCustomer.SalesOrderHeaders.Count); This call to Include asks to load related entities available through the Customer entity s SalesOrderHeaders property. (These will be loaded regardless of the lazy loading setting.) It also says that for each of those related entities, the EF should load any related entities visible through the SalesOrderDetails property. In other words, this tells the EF that we would like it to fetch all of the orders for this customer and all of the details for those orders. It will generate a single query that fetches all of the necessary information in one request. We chose the Text File template because we don t want any of the built-in functionality provided by something like a Web Form template; we need only a blank file. Inside our base layout, we need to place a couple of links and provide a placeholder for the actual child content. Our entire layout is shown in listing 10.14. Creating your layout . ................................................................................................... 175 Planning your theme. .................................................................................................. 176 Theme settings . If you re wondering why it doesn t just prefetch all related items all of the time, consider the performance implications. In some circumstances, aggressively prefetching all related items might amount to attempting to copy a significant fraction of your database into memory! But even in more circumscribed cases, fetching more data than you need can slow your system down or reduce scalability. So far we have seen only so-called one-to-many relationships one customer can be related to many orders, one order can be related to many order details. But there are other kinds of relationships. <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Spark View Example</title> <link href="~/Content/Site.css" rel="stylesheet" type="text/css" /> </head> <body> <div class="page"> <div id="header"> <div id="title"> <h1>My MVC Application</h1> </div> <div id="logindisplay"> Welcome! </div> <div id="menucontainer"> <ul id="menu"> <li>${Html.ActionLink("Home", "Index", "Product")}</li> </ul> </div> </div> The multiplicity of a relationship refers to the number of participants at either end of the association. In the Entity Framework, an association s multiplicity determines the nature of the navigation properties that represent the relationship. In the Entity Framework, there are always two ends to an association, regardless of the multiplicity. For example, we have customers at one end of a relationship and orders at the other end. The multiplicity describes how many items may be at a particular end, not how many ends there are. You will sometimes want to represent more complex relationships for example, a so-called ternary relationship involves three kinds of parties. This is a different concept from multiplicity and is called degree. For example, consider a teaching arrangement in a college, where a student is taught a subject by a teacher; this relationship involves three entities (student, subject, and teacher). These higher-degree relationships are typically modeled in the database by having a table just for the relationship itself. Likewise, the EDM does not directly support relationships with a degree of more than two, so you would represent such a relationship with a distinct entity type in the conceptual model, adding associations between that entity and all the participants in the relationship. For each end of a relationship, you can specify a multiplicity of either 1, 0..1, or *. The first, 1, means what it says there is always one item at that end of the association. The last, *, means any number there can be zero, one, or several items at that end. A multiplicity of 0..1 means zero or one this indicates that the association is optional, but where present, there is just one entity at this end. In a one-to-many relationship, the two ends have a multiplicity of 1 and *, respectively. You can see this in Figure 14-2 the lines between entities represent associations, and the multiplicity appears at each end of the line. So an item at the first end can be related to any number of items at the second end; an item at the second end is always related ........................................................................................................ 176 ......................................................................................................... 182
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