chapter 15: using linq to access data in c# programs
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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 - PowerPoint PPT PresentationTRANSCRIPT
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
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Understanding Relational Database Fundamentals (cont’d.)
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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
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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
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Creating Databases and Table Descriptions (cont’d.)
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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
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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"
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Creating an Access Database
• Microsoft Office Access– A relational database that is part of some versions of the
Microsoft Office system
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Creating an Access Database (cont’d.)
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Creating an Access Database (cont’d.)
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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
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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
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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
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Retrieving Data from an Access Database in C# (cont’d.)
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Retrieving Data from an Access Database in C# (cont’d.)
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Retrieving Data from an Access Database in C# (cont’d.)
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Retrieving Data from an Access Database in C# (cont’d.)
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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
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Using LINQ Queries with an Access Database Table (cont’d.)
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Using LINQ Queries with an Access Database Table (cont’d.)
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Using LINQ Queries with an Access Database Table (cont’d.)
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Using LINQ Queries with an Access Database Table (cont’d.)