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

Chapter 15:Using LINQ to Access Data in

C# Programs

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


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



• 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


Creating Databases and Table Descriptions (cont’d.)


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


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"


Creating an Access Database

• Microsoft Office Access– A relational database that is part of some versions of the

Microsoft Office system


Creating an Access Database (cont’d.)


Creating an Access Database (cont’d.)


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


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


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


Retrieving Data from an Access Database in C# (cont’d.)








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


Using LINQ Queries with an Access Database Table (cont’d.)







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