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Chapter 15: Using LINQ to Access Data in C# Programs.

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Presentation on theme: "Chapter 15: Using LINQ to Access Data in C# Programs."— Presentation transcript:

1 Chapter 15: Using LINQ to Access Data in C# Programs

2 2Microsoft Visual C# 2012, Fifth Edition Understanding Relational Database Fundamentals Database – Holds a file or, more frequently, a group of files that an organization needs to support its applications In a database, the files often are called tables because you can arrange their contents in rows and columns Primary key (or key) – A value that uniquely identifies a record

3 3Microsoft Visual C# 2012, Fifth Edition Understanding Relational Database Fundamentals (cont’d.)

4 4Microsoft Visual C# 2012, Fifth Edition Understanding Relational Database Fundamentals (cont’d.) Database management software – Also called a database management system (DBMS) – Allows you to: Create table descriptions Identify keys Add, delete, and update records within a table Arrange records within a table so they are sorted by different fields Write questions that select specific records from a table for viewing Write questions that combine information from multiple tables Create reports that allow users to easily interpret your data Keep data secure by employing sophisticated security measures

5 5Microsoft Visual C# 2012, Fifth Edition Understanding Relational Database Fundamentals (cont’d.) Database management software (cont’d.) – Establishes and maintains relationships between the columns in tables A group of database tables from which you can make these connections is a relational database

6 6Microsoft Visual C# 2012, Fifth Edition Creating Databases and Table Descriptions (cont’d.)

7 7Microsoft Visual C# 2012, Fifth Edition Identifying Primary Keys The primary key in a table is the column that makes each record different from all others – Each primary key must be unique Typical examples of primary keys include: – A student ID number in a table that contains college student information – A part number in a table that contains inventory items – A Social Security number in a table that contains employee information

8 8Microsoft Visual C# 2012, Fifth Edition Creating SQL Queries Query – Simply a request using syntax that the database software can understand Structured Query Language (or SQL) – The most common language that database administrators use to access data in their tables The basic form of the SQL command that retrieves selected records from a table – SELECT-FROM-WHERE Example: SELECT custId, lastName FROM tblCustomer WHERE state = "WI"

9 9Microsoft Visual C# 2012, Fifth Edition Creating an Access Database Microsoft Office Access – A relational database that is part of some versions of the Microsoft Office system

10 10Microsoft Visual C# 2012, Fifth Edition Creating an Access Database (cont’d.)

11 11Microsoft Visual C# 2012, Fifth Edition Creating an Access Database (cont’d.)

12 12Microsoft Visual C# 2012, Fifth Edition Understanding LINQ LINQ (Language INtegrated Query) Project – Provides queries that can be used in C# and Visual Basic In older versions of C#, you could access database data by passing an SQL string to a database object – OleDbCommand is a built-in type used to access databases LINQ provides a set of general-purpose standard operators that allow queries to be constructed using syntax that is easy to understand

13 13Microsoft Visual C# 2012, Fifth Edition Understanding LINQ (cont’d.) The operators defined in LINQ can be used to query arrays, enumerable classes, XML, relational databases, and other sources Some keywords in the LINQ vocabulary: – select indicates what to select – from indicates the collection or sequence from which data will be drawn – where indicates conditions for selecting records

14 14Microsoft Visual C# 2012, Fifth Edition Retrieving Data from an Access Database in C# Save time and reduce the chance for error by using the built-in tools of the Visual Studio IDE Tasks for adding a database table to a Windows Form project: – Drag a DataGridView object from the IDE’s Toolbox onto a Form Next, browse for the project data source and answer a few questions – Make a few choices and browse for the database file to add to the project

15 15Microsoft Visual C# 2012, Fifth Edition Retrieving Data from an Access Database in C# (cont’d.)

16 16Microsoft Visual C# 2012, Fifth Edition Retrieving Data from an Access Database in C# (cont’d.)

17 17Microsoft Visual C# 2012, Fifth Edition Retrieving Data from an Access Database in C# (cont’d.)

18 18Microsoft Visual C# 2012, Fifth Edition Retrieving Data from an Access Database in C# (cont’d.)

19 19Microsoft Visual C# 2012, Fifth Edition Using LINQ Queries with an Access Database Table You are not required to use the data grid to view database records You can use a LINQ query to select a collection of data from a table when specific criteria are met

20 20Microsoft Visual C# 2012, Fifth Edition Using LINQ Queries with an Access Database Table (cont’d.)

21 21Microsoft Visual C# 2012, Fifth Edition Using LINQ Queries with an Access Database Table (cont’d.)

22 22Microsoft Visual C# 2012, Fifth Edition Using LINQ Queries with an Access Database Table (cont’d.)

23 23Microsoft Visual C# 2012, Fifth Edition Using LINQ Queries with an Access Database Table (cont’d.)


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