Transcript Lecture

Lecture 14 A new
Introduction to Databases: DB
Review & ADO.NET Models –
Connected and Disconnected
By Chris Pascucci and FLF
Introduction to Databases
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A database is a collection of data related to a particular topic.
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Databases can range from a few kilobytes to several terabytes and beyond.
The Integrated Student Information System (ISIS) used at Temple University
is a large database. So is Banner, if it would ever work right.
Google’s database is an example of a massive database.
NSA has a massive database called a data warehouse that collects information
from a variety of other databases.
Social Security has massive data base – imagine what is stored here
And then … there will be the Affordable Care Act data base …
A Database Management System (DBMS) is software that is
used to create, access and maintain a database.
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Microsoft Access
Microsoft SQL Server
Oracle
Introduction to Databases
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A relational database stores data and the connections
(relationships) within the data.
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A relational database uses tables to store data and
manipulate it.
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A table can be visualized as a 2-dimensional grid that contains rows
and columns.
Each table contains one or more records (rows) that
contain information about a single entry.
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It uses a relational data model.
Records contain a set of related fields that are used to store data.
Each record contains one or more fields (columns) that
contain a single piece of data.
Introduction to Databases
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More TERMINOLOGY …
A table represents an entity in a problem domain.
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For example, in the integrated system information system ISIS, a
table may represent a student entity or a course entity
A record is an instance of an entity.
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In ISIS, a specific student record (you, for example) would be an
instance of the student entity (table).
Also, a specific course “CIS3309 Section 001” would be an instance of
the course entity.
Database Tables are models of application domain entities – those
“things” that need to be manipulated in our system
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These things are no different in concept from the entities we model in C#
Only here we use classes for our models rather than database Tables
Introduction to Databases
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Most tables include a primary key, which is a field that
uniquely identifies each record in a table.
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Storing student records by name in a large university will make it
difficult to find students with the same name. Giving each student a
StudentID uniquely identifies each student.
SSN uniquely identify each American in the U.S.
The tables in a relational database are related to each
other through their key columns. A column that
identifies a related row in another table is called a
foreign key.
Illustration – Primary and Foreign Keys
Product Table
Intro to Databases – Naming Conventions
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A database named Employees with one table named
tblEmployees containing the following fields:
fldEmployeeID – (number) unique employee id number
fldFirstName and fldLastName – (strings) employee's first and last name,
respectively
fldTelephone – (string or number) the employee's telephone number
fldDateHired – (date value) stores date that the employee was hired
fldWage – (number) contains the hourly wage for the employee
fldDeductions – (number) contains the number of tax deductions claimed by
the employee
fldNotes is a string containing notes pertaining to the employee
fldStatus – (Boolean) If True the employee is still employed. If False the
employee is a former employee.
fldType – (string) employee (valid values: fulltime and parttime)
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Populated Database Table
Naming Database Tables and Fields
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Standard (Hungarian) prefixes are commonly
used to name database tables and fields
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The prefix "tbl" denotes a table
The prefix "fld" denotes a field
Relational Databases
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Data stored in one table can be related to data stored
in another table in a few ways:
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One-To-One Relationship
One-To-Many Relationship.
Many-To-Many Relationship.
One-To-Many Relationship means a record in one table
is related to many records in another table via primary
and foreign keys.
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For example, a course record in the Course table for Temple
university can relate to many students in the Student table.
Relational Databases
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Many-To-Many Relationship means a record in Table A
can have many records in Table B, and vice versa.
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It can be thought of as two separate one-to-many relationships.
For example, a writer can write many books, and a book can have
many writers.
Thus, a Book table can contain a record that relates to an Author
table by having multiple authors for a book, and an author record in
the Author table can relate to the Book table by having a author that
wrote many books.
Student-course example?
What do we do to many-many relationships? One-many. Many-one.
One-To-One Relationship means a record in one table
is related to one and only one record in another table.
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For example, an employee has a single resume, and each resume
only belongs to one employee.
Introduction to SQL
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Structured Query language (SQL) is an English – like
language that is used to manage and manipulate data
in the database.
There are 4 basic SQL statements that are needed to
work with data in a database.
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SELECT – used to query a table and find specific information based on
some criteria. It selects one or more rows (records) from a table.
INSERT – used to add one or more rows (records) to a table.
UPDATE – used for modifying data in one or more rows (records) in a
table.
DELETE – used to delete one or more rows (records) in a table.
SQL: Select Statement
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The result of a Select statement is called a result set, or
result table, which is a logical set of rows that consists of
all of the columns and rows requested by the Select
statement.
Syntax:
SELECT column_name [, column_name2]...
FROM table_name
[WHERE selection-criteria]
[ORDER BY column_name [ASC|DESC] [, column_name2[ASC|DESC]]...]
SQL: Select Statement Example
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Example:
SELECT ProductID, Name, UnitPrice
FROM Products
WHERE CategoryID = “props”
ORDER BY UnitPrice DESC
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The asterisk (*) can be used
to select all fields of a table.
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Example:
SELECT * FROM Products
Result Set shown above.
Click button to view full table.
SQL: Insert Statement
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The Insert statement is used to add a new row (record)
to a table. It can be used to set fields to specified values
as it adds the new record.
Syntax:
INSERT [INTO] table_name [(columns_list)]
VALUES (values_list)
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The order of the items in columns list must match the
order of the items in the values list.
SQL: Insert Statement Example
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Example:
INSERT INTO Products (ProductID, ShortDescription, UnitPrice)
VALUES (“p101”, “Toy”, “19.99”)
SQL: Update Statement
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The Update statement is used to modify/edit existing
data within a table.
Syntax:
UPDATE table_name
SET column_name = value [, column_name2 = value 2]...
WHERE selection-criteria
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Syntax:
UPDATE Products
SET UnitPrice = “25.79”, OnHand = “3”
WHERE ProductID=“arm01”
SQL: Delete Statement
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The Delete statement is used to remove a row or rows
from a table.
Syntax:
DELETE FROM table_name
WHERE selection-criteria
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Example:
DELETE FROM Products
WHERE ProductID = “arm01”
SELECT Example
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Table used in SQL Examples:
Return to last
viewed slide
Introduction to DB Access in VS - ADO.NET
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The ActiveX Data Objects (ADO.NET) is part of the
.NET framework that provides a multi-layered set of
data access namespaces (set of classes), which allow
us to access and modify data stored in a database.
ADO.NET is the primary data access API for the .NET
framework.
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It is a framework inside a framework.
This framework’s responsibility is to allow our programs to work with
databases by providing the abstraction against which we can program
ADO.NET supports many different database platforms
ADO.NET supports both a connected and disconnected
data architecture.
ADO.NET Libraries
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ADO.NET supports multiple database platforms
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SqlClient provides support for Microsoft SQL Server 7.0 and
later.
 System.Data.SqlClient
OracleClient provides support for Oracle 8.1.7 and later.
 System.Data.OracleClient
OleDb (Object Linking & Embedding) provides support for
conecting to OleDb sources like SQL server, Oracle, and
Microsoft.ACE.OLEDB.12.0 (Microsoft Access).
 System.Data.OleDb
ODBC (Object Database Connection) provides support for connection to
ODBC source. Only used when you are not connecting to an OleDb source.
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System.Data.ODBC
Database Providers
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Object Linking & Embedding Database (OLE DB)
connectivity system based on Active X technology.
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In .NET, ODBC and OLE DB are replaced by “providers”
called Data Providers
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ActiveX is Microsoft technology used for developing reusable objectoriented software components.
Libraries of code provide all necessary communication between your
code and database systems.
Providers are an integral part of ADO.NET.
Providers exist for the main database systems such as SQL Server,
Access, and Oracle.
For this course, we will be working in the provider
world mostly with SQL Server or Access providers.
The ADO.Net Platforms
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Microsoft ACE Database Engine is now the main Accessbased component for storing, parsing, optimizing, and
processing queries.
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ACE (Access Connectivity Engine -- now called the Access Database
Engine) - successor to the Jet (Joint Engine Technology) model
Newest database engine for working with Access 2007 (and later)
“.accdb” files.
JET - the database engine used for Microsoft Access 2003 and earlier.
It is a File-Server System DBMS where the work is done on the individual
computer where the Access DBMS exists.
Microsoft SQL Server is a client-server DBMS in which the
client requests information from the database and the
server processes the request.
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Provides functionalities beyond those available through JET.
Improved multi-user access and transaction-based processing.
The ADO.NET Platforms - 2
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Oracle is another client-server DBMS used for large
databases.
Visual Studio & .NET have tools for working with all
these database management systems.
These tools are part of the sub-namespaces of the
System.Data namespace
More on ADO.NET
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ADO.NET has three main abstractions:
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The ADO.NET DataProviders are components
(namespaces containing classes) specifically designed
for working with a particular database platform.
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There is a namespace (a set of classes) for working with Access, SQL
Server, one set specifically for Oracle, etc…
The ADO.NET DataSet is a component used for working
with data separate from the data source.
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DataProviders
DataSets
DataReaders
An integral part of the disconnected data architecture.
The ADO.NET DataReader is an abstraction that is the main
feature for working in the connected mode of DB processing
ADO.NET Components
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The DataAdapter is a component that is used to load
data into the DataTable of a DataSet.
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Data Adapter’s major function is to manage the exchange of data
between the database and the DataSet.
The Command component is used to issue SQL
commands for the DataAdapter to execute while
connected to a database.
The Connection component is used to establish a
connection to a database for the DataAdapter to use.
The DataReader component is used for read-only,
forward-only stream of data coming from a database.
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This component is part of a connected data architecture.
Still More on ADO.NET
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We can consider the Data Adapters and Data
Readers as providing two distinct models of
access to data bases provided in .NET
For an introduction to some of the distinctions
between these two models, visit …
http://msdn.microsoft.com/enus/library/ms254931%28v=vs.110%29.aspx
Disconnected vs. Connected
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The major advantage of the disconnected approach is
that it improves system performance due to the fact
that it uses less resources for maintaining connections
when working with a data source.
However, there is a disadvantage to this approach that
occurs when two or more users try to update the same
row of a table, which is called a concurrency problem.
Database server
User 1
DBMS
User 2
Products
data table
Products
table
Products
data table
Disconnected vs. Connected
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ADO.NET contains two different approaches to work with data in a
database: Connected Data Architecture and the Disconnected Data
Architecture.
Connected Data Architecture:
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Represents the objects that insist on having an open connection available for
them to work and interact with the data source.
ADO.NET provides classes to communicate directly with a data source.
Disconnected Data Architecture:
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Represents the objects that open and close a connection to the data source as
needed.
Your application works with data that was copied from the data source. Any
changes made to the “copied” data in the Dataset will be later reconciled with
the data source.
Connected applications alone don't fulfill the demands of today’s distributed
applications.
Improved performance, more efficient and more complex than the connected
approach.
Disconnected vs. Connected
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Concurrency problems occur because once data is retrieved from
the database, the connection is dropped. As a result, the DBMS
can’t manage the update process.
There are two ways that ADO.NET can handle concurrency
problems:
1. Optimistic Concurrency – The program checks to see if there has
been a change to the row since it was retrieved. If it has, the update
or deletion will be refused and a concurrency exception will be
thrown that your program must handle.
2. “Last In Wins” – Since no checking is done, the row that was
updated by the last user will overwrite changes made to the row by
the previous user.
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Another way to avoid concurrency problems is to retrieve and
update only one row at a time.
ADO.NET Explained
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ADO.NET Components for Disconnected Approach:
Dataset
.NET data provider
Data table
Data adapter
Command
Database server
Connection
Database
ADO.NET Explained
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ADO.NET Components for the Connected Approach:
.NET data provider
Data reader
Select command
Database server
Connection
Insert, Delete, or
Update command
Database
Steps to Working with ADO.NET
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First, a database connection is established
Then the database is opened
SQL commands are sent over the open connection
ADO.NET builds an in-memory representation of the
returned data from any SELECT command and changes
are made to this representation
When processing is complete, the database connection is
closed
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It is suggested that you use the Open and Close methods to
explicitly open and close your connections. In this way, you
keep your connections open only as long as needed to
complete the required processing
This is true for both the connected and disconnected models
But the definition of when “processing is complete” will differ
Processing Database Elements
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All elements of a data base, tables (entities),
rows (sets of values), columns (database
fields), and individual cells (database values)
are represented as abstractions in .NET
In other words, every table, row, and column
are represented as instances of the
abstractions (classes) that are part of the
ADO.NET support structure
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But the abstractions you “program against” using
DataReaders are different from those involved
when using DataSets
We will see how all this fits together later
An Underlying Framework –
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The Connection
Keeping a mental picture of this process in your head is
important
It all begins with the connection
Already visited this idea for files and graphics. Now we
revisit it a third time for databases
Remember …
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In your programs, you manipulate objects using methods
belonging to the class that defines the type of the object
The class (an abstract data type) is an abstraction (model)
of the object being manipulated
The Object Framework 1
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Recall, too …
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We must have a class to model the entity to be
manipulated
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The class is said to define an “abstract data type”
We can then create objects (instances of the class
we just created)
Next comes the tricky part …
We now have to connect that object to the
actual entity to be drawn on
The Object Framework 2
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For databases, the object is an instance of a class
that provides an abstract view of the database
including an abstraction of database tables, rows,
and columns
All of these database features are modeled using
ADO.NET classes
So we program against elements of the ADO.NET
classes (see the first slide on ADO.NET) without
concern for the underlying structures
The Object Framework 3 – The Connection
The database
abstraction
(methods and data
stores) that you
program against
(DB commands,
internal datasets
and data tables)
The
connection –
via creation
of a database
connection
object
The actual,
physical
database to be
manipulated
‘Example - Connection to a Microsoft Access Database
OleDbConnection myAccConnectionObj = new OleDbConnection(connectString);
‘Example - Connection to SQL Server Database
SqlConnection mySqlConnectionObj = new SqlConnection(connectString);
Remember …
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Why do this – what is this all about?
The abstraction enables us to manipulate
database objects in a uniform, consistent way,
regardless of the DBMS (Access, MySQL, SQL
Server, Oracle)
The underlying DBMS is hidden under several
layers of ADO.NET software which do all the
work
Connection Strings – more details 1
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We need to connect the program’s ADO.NET database object to the underlying
database to be used
// SQL Server Connection
string connectString = "server=dwarf.cis.temple.edu;Database=fa06_c342132;” +
"User id=fa06_c342132;Password=jimbo“;
SqlConnection myConnectionSql = new SqlConnection(ConnectString)
// Access Connection
string connectString = "provider=Microsoft.ACE.OLEDB.12.0;” +
“Data Source=c:\users1\dl\Inventory.accdb“
OleDbConnection myConnection = new OleDbConnection(ConnectString)
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Programmer layer – build commands (SELECT, INSERT, DELETE, and UPDATE)
for execution against the database
Logical layer – uses a DataAdapter to send commands from your software
(across the data adapter) to the database getting back tables to be processed
(we will visit this in a later section of the Chapter 11 Lectures)
Physical layer – manages the actual (physical) execution of the commands on
the database
A connection string …
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A connection string consists of key-value pairs
An equals sign separates a key and value
A semicolon separates a key-value pair
Connection strings differ for each database provider
Connection Strings – more detail 2
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Documentation for Visual Studio contains
includes an article entitled “Working with
Connection Strings” which you can find by
using on-line help index “connection strings
[ADO.NET]”
You can also go to
http://www.connectionstrings.com
to locate lots more information about
connection strings
The OleDbConnection Class
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A connection is represented by the
System.Data.OleDb.OleDbConnection class
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Properties
The ConnectionString property contains a string that determines how
ADO.NET will establish the database connection. One of the benefits of
ADO.NET is that if a program is migrated to use a different database, all
of the other code remains intact. Only the ConnectionString needs to be
changed.
 The ConnectionTimeout specifies the number of seconds that can
elapse to establish a connection.
 The DataSource property gets the location and file name of the
database. This file name is embedded into the ConnectionString.
 The Provider property defines the database provider. This information is
also embedded into the ConnectionString property.
 The State property gets the state of the connection.
A Few Methods
 The Open and Close methods open and close the connection,
respectively.
An Event
 The StateChanged event fires when the connection state changes.
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Database Processing Sequence
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Establish a connection to your data source using the
Connection object.
Create an SQL command statement either using a
string or the Command object.
Execute the Command object within the context of the
connected database.
Process the results of the commands by
retrieving/storing the data when necessary.
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Use the DataReader to read the records.
Use the DataAdapter and DataSet for storage of data retrieved from
the database, and for use in your program.
Close the connection and release resources utilized by
all the objects.
ADO.NET Terms Summary
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DataSet:
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DataAdapter:
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Executes commands (SQL statements) against the data source.
Data Providers:
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Connects to the data source.
Command:
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Manages the exchange of data between the Dataset and a database.
Allowing a DataSet and DataTable to be filled from the data source and later
reconciled with the data source.
Connection:
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Data in the Dataset is independent of the database that was used to retrieve it.
The ADO.NET classes responsible for working directly with a specific database.
Data Reader
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Retrieves query results in a read-only, forward-only connected result set.
ADO.NET Resources
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Connection Strings:
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OleDbConnection Class:
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http://msdn.microsoft.com/en-us/library/system.data.oledb.oledbcommand.aspx
OleDbDataAdapter Class:
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http://msdn.microsoft.com/enus/library/system.data.oledb.oledbconnection.aspx
OleDbCommand Class:
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http://www.connectionstrings.com
http://msdn.microsoft.com/enus/library/system.data.oledb.oledbdataadapter.aspx
OleDbDataReader Class:
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http://msdn.microsoft.com/enus/library/system.data.oledb.oledbdatareader.aspx