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Chapter 15: Using LINQ to Access Data in C# Programs. Understanding Relational Database Fundamentals. Database Holds a file or, more frequently, a group of files that an organization needs to support its applications

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Chapter 15 using linq to access data in c programs

Chapter 15:

Using LINQ to Access Data in C# Programs


Understanding relational database fundamentals
Understanding Relational Database Fundamentals

Microsoft Visual C# 2012, Fifth Edition

  • 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
Understanding Relational Database Fundamentals (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Understanding relational database fundamentals cont d1
Understanding Relational Database Fundamentals (cont’d.)

Microsoft Visual C# 2012, Fifth Edition

  • 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


Understanding relational database fundamentals cont d2
Understanding Relational Database Fundamentals (cont’d.)

Microsoft Visual C# 2012, Fifth Edition

  • 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
Creating Databases and Table Descriptions (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Identifying primary keys
Identifying Primary Keys

Microsoft Visual C# 2012, Fifth Edition

  • 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
Creating SQL Queries

Microsoft Visual C# 2012, Fifth Edition

  • 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
Creating an Access Database

Microsoft Visual C# 2012, Fifth Edition

  • 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.)

Microsoft Visual C# 2012, Fifth Edition


Creating an access database cont d1
Creating an Access Database (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Understanding linq
Understanding LINQ

Microsoft Visual C# 2012, Fifth Edition

  • 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
Understanding LINQ (cont’d.)

Microsoft Visual C# 2012, Fifth Edition

  • 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
Retrieving Data from an Access Database in C#

Microsoft Visual C# 2012, Fifth Edition

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

Microsoft Visual C# 2012, Fifth Edition


Retrieving data from an access database in c cont d1
Retrieving Data from an Access Database in C# (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Retrieving data from an access database in c cont d2
Retrieving Data from an Access Database in C# (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Retrieving data from an access database in c cont d3
Retrieving Data from an Access Database in C# (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Using linq queries with an access database table
Using LINQ Queries with an Access Database Table

Microsoft Visual C# 2012, Fifth Edition

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

Microsoft Visual C# 2012, Fifth Edition


Using linq queries with an access database table cont d1
Using LINQ Queries with an Access Database Table (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Using linq queries with an access database table cont d2
Using LINQ Queries with an Access Database Table (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


Using linq queries with an access database table cont d3
Using LINQ Queries with an Access Database Table (cont’d.)

Microsoft Visual C# 2012, Fifth Edition


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