Lab Objective Estimated time to complete this lab: 60 minutes The objective of this lab is to gain a clear understanding of the LINQ project. You will see how data manipulation can occur on objects in memory, database tables, and XML files.
A brief look at query operators will be. Keep in mind that the IDE support and compiler are preview releases, and still have many flaws. A consequence is that incorrect code may result in an abundance of error messages. It is important to address errors top-down, then recompile as spurious errors will often disappear once valid ones are addressed. In this exercise, you will learn how to query over object sequences. Any collection supporting the generic interface System.
Support is also included for types defined using System. Standard Query Operators allow programmers to construct queries as well as projections that create new types on the fly. This goes hand-in-hand with type inference, a new feature that allows local variables to be automatically typed by their initialization expression.
Click the Tools Options menu command 3. In the left hand treeview select Debugger General 4. Click OK 6. Click the File New Project menu command 7. Click OK. In Solution Explorer, double click Program. This is possible due to one of the new features of LINQ: the inference of type information, where possible, directly by the compiler. In this case the right-hand side specifies that the type is int[]; therefore the type of numbers is inferred to be int[]. This is often convenient for initialization expressions because it allows the type name to be specified only once.
As in the previous step, type inference is being used here to simplify the code. The return type from a query may not be immediately obvious. This example is returning System. IEnumerable , but many queries return structured results with no obvious declared type; indeed, sometimes. In these cases type inference can be particularly useful. The final line, Console. ReadLine , is used to prevent the console window from disappearing until enter is pressed.
Press F5 to launch the application. A console window will appear. As intended all even numbers are displayed the numbers 4, 2, and 8 appear in the console output. The call to the Console. ReadLine method prevents the console window from disappearing immediately. In subsequent tasks, this step will not be stated explicitly. In this task, you will move beyond primitive types and apply the query features to custom structured types.
In the past this would require consumers to create an instance of the object using the default parameterless constructor and then set the fields explicitly as separate statements. First of all, notice that the new collection is being populated directly within the curly braces. Second, notice that the Person elements are being created with a new syntax known as object initializers.
Even though there is no constructor with two parameters for the Person class, it is possible to create objects of that class as expressions by setting its fields explicitly inside curly braces.
Finally, notice that there is no need to specify every field explicitly, rather only those which need to be set are stated. For example, the third element only sets the Age field of the Person.
The Name property will retain its default value of null. Next query the collection for teenagers. Add the following query code:. Name, val. Add a call to the ObjectQuery method in the Main method and remove the call to NumQuery : static void Main string[] args. Press F5 to debug the application. Two results are shown. The first result shows that the name is Cindy, but the second result shows no name.
This is the expected output since the Name field of that object was never initialized. As you can see, working with complex types is just as easy as working with primitive types using LINQ query expressions. NET that supports Language Integrated Query, allowing you to query and manipulate objects associated with database tables. Task 1 — Working with DLinq 7. The first step is to create business objects to model the tables.
To simplify the lab, the Northwind table definitions will be imported from an external file. The code is easy to understand, but tedious and error-prone to generate. Once the definitions are in-place accessing the tables is easy. Click Add In Program. This is not necessary for in-memory LINQ queries but, in the case of DLinq, it adds additional support for accessing the underlying database tables.
Scroll down to the public partial class Category Each type definition relates to a given database table. This allows data to be retrieved and manipulated consistently from the underlying table, while allowing client code to treat it strictly as objects. Task 2 — Querying using Expressions Each table is now accessed as a property of the db variable.
At this point, querying is identical to the previous exercise. Customers where c. Displaying the matching customers is straightforward. Add the following code:. CompanyName, cust. ContactName, cust. Thirteen results are shown. So far, the queries have been primarily based on filtering; however, LINQ supports many options to query data beyond filtering.
The same thirteen results are shown, but notice that the order is now determined by the alphabetical ordering second displayed field, ContactName. It is also possible to use built-in string methods in queries. Contains "Market" orderby c. Task 3 — Querying using the Standard Query Operators LINQ also introduces various Standard Query Operators to achieve the same functionality using a more traditional object-centric approach.
The "c" becomes the parameter to an unnamed method. The c. Contains "Market" expression can be thought to have an implicit return statement preceding it. The query is now calling the Standard Query Operators, but the results are the same, as is the procedure for working with the results. Aggregates of data can be produced by simply calling the Standard Query Operators on the result just as you would any other method.
StartsWith "A". Average ; Console. In addition to the customers the results now show the average cost for products starting with "A". If this is read from left to right, it would read as, specify the table db. Products and restrict the results to those with product names which begin with "A". This first step, by itself, simply returns a filtered result set of Products matching the criteria. Next, select the UnitPrice column which returns a collection of prices, one for each original result.
The final. In this exercise, you will learn how to read XML documents into the XDocument object, how to query elements from that object, and how to create documents and elements from scratch. Task 1 — Adding XLinq Support The project template used earlier takes care of adding references and using directives automatically.
XLinq reference. Creating full-fledged documents from scratch requires instantiating the XDocument object then appropriate XElement, XAttribute and other entities as required for the document. The simplest action to take is to display the document.
WriteLine doc ; Console. As you can see, creating the document required few steps, and can be accomplished in a single line of code The next step is to query the document. You will learn to absorb criticism and use it to improve. I was determined that I would stay with it till 31st December Psychological wellbeing is the worst option with respect to this issue. The wall runs from the Octagonal pond to the bastion on the south-east, which is formed of wide brick walls linking a series of boulders surrounding a cave pavilion with a rock-cut throne.
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