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ADO.NET
Andrei Otcheretianski
Tomer Rothschild
Contents


Introduction

What is ADO.NET?

Data Access
Motivation - Why Moving to ADO.NET?

ADO.NET Objects
 Content components
 Managed-provider components
 ADO.NET & Transactions

ADO.NET and XML

.NET Framework Data Providers

ADO.NET 2.0 Added Features

Summary - Pros & Cons
February 2nd, 2006
ADO .NET
2
What is ADO.NET?

ADO.NET (ActiveX Data Objects) is the primary relational data
access model for Microsoft .NET-based applications.

The data access objects role is to serve as an interface between
the client application and the data provider – the DBMS. This
modularity results in two big advantages:


Allowing the writing of applications that use standard types
and features, resulting in DBMS independent code.
Unified API for the database driver implementers.
February 2nd, 2006
ADO .NET
3
Things Weren’t Always So Simple…

Let’s have a Brief Look at the evolution that lead to ADO.NET
 At first, programmatic access to databases was performed by
native libraries, such as DBLib for SQL Server, and the Oracle
Call Interface (OCI) for Oracle.


This allowed for fast database access because no extra layer
was involved.
However, it also meant that modularity was absent. i.e. loosing
the two advantages discussed on the previous slide.
February 2nd, 2006
ADO .NET
4
Data Access Evolution

(1)
ODBC:
As a solution, Microsoft and other companies developed the
Open Database Connectivity, or ODBC.

This provided a common data access layer, which could be used
to access almost any relational database management system.

In practice, there were some differences in the SQL dialect
supported hence, violating the main principle of modularity.

Nonetheless, perhaps the most important feature of ODBC is the
fact that it was an open standard, widely adopted even by the
Open Source community.
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ADO .NET
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Data Access Evolution

DAO:



(2)
As the importance of Visual Basic grew, there was a need for a
data access technology that could be used more naturally from
VB.
DAO (Direct Access Objects) provided a simple object model for
talking to Microsoft's Access desktop database. As DAO was
optimized for Access, it was very fast.
RDO:


Due to its optimization for Access, DAO was very slow when
used with ODBC data sources. To get round this, Microsoft
introduced Remote Data Objects (RDO).
RDO was designed specifically for access to ODBC data
sources. RDO is essentially a thin wrapper over the ODBC API.
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ADO .NET
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Data Access Evolution

OLE DB:


(3)
As part of the OLE (Object linking and Embedding) distributed
object system, the OLE DB is used for accessing different types
of data stores in a uniform manner.
ADO:



ActiveX Data Objects is the technology that gave its name to
ADO.NET (although in reality the differences are far greater than
the similarities).
ADO is merely an OLE DB consumer – a thin layer allowing
users of high -level languages to access OLE DB through a
simple object model.
In a way, ADO is to OLE DB more or less what RDO was to
ODBC
February 2nd, 2006
ADO .NET
7
Why Moving to ADO.NET?

Why not simply continue to use ADO in the .NET framework?
 It's perfectly possible to carry on using ADO in .NET
applications through COM interoperability.
 However, there are some very good reasons why ADO wasn't
really suited to the new programming environment:





Using Managed Classes
Cleaner Architecture
Cross-Language Support
XML Support
Optimized Object Model
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ADO .NET
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Why Moving – Managed classes &
Cleaner Architecture

Using Managed Classes
 The alternative - using .NET then COM interoperability - adds
overhead to the application.
 Takes advantage of the benefits of the CLR such as JIT
compilation and the managed execution environment.

Cleaner Architecture
 As we noted above, ADO is no more than a thin layer over
OLE DB.
 ADO.NET can be much faster than ADO, as the providers
communicate directly with the data source.
February 2nd, 2006
ADO .NET
9
Why Moving – Cross-Language Support
& XML Support

Cross Language Support
 ADO was aimed primarily at VB programmers. This lead to
using optional method parameters, which are not supported
by C-based languages such as C#.
 This means that if you use ADO from C#, you will need to
specify all parameters in method calls. This makes ADO
programming under .NET considerably more time-consuming

XML Support
 XML is absolutely integral to ADO.NET, and not just an addon.
 As we shall see later on in the demo, XML is the format used
to serialize and transport DataSets.
February 2nd, 2006
ADO .NET
10
Why Moving – Optimized Object Model

Optimized Object Model
 The .NET Framework is aimed squarely at developing
distributed applications, and particularly Internet-enabled
applications.

In this context, for example, we don't want to hold a
connection open for a long time, as this could create a
bottleneck and destroy scalability.

ADO didn't encourage disconnected recordsets, whereas
ADO.NET has different classes for connected and
disconnected access, and doesn't permit updateable
connected recordsets.
February 2nd, 2006
ADO .NET
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ADO .NET - Objects
DataSet
.Net Data Provider
Connection
Transaction
Command
Parameters
DataReader
Data Adapter
Select
Data Table
Insert
DataColumn
Constraints
Update
DataRow
Delete
DataRelations
<XML>
DB
February 2nd, 2006
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ADO .NET – Objects(2)

In ADO .NET there are two class groups.

Content components

Managed-provider components
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ADO .NET
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ADO .NET – Objects(3)

Content components


The content components hold actual data and include
 DataSet
 DataTable
 DataView
 DataColumn
 DataRow
 DataRelation
Managed-provider components

These components actually talk to the database to assist in data
retrievals and updates. Such objects include the Connection,
Command, Data Reader and Data Adapter.

The managed-provider components are split into several groups
designed for each provider as we will see later.
February 2nd, 2006
ADO .NET
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Connection

Connection

Provides a connection to the database . There are typical Open() and
Close(), plus BeginTransaction() returning an object to control a
database transaction.

To open a connection to a data source you need to provide a
connection string.


Example:
"Network Library=DBMSSOCN; Data Source=132.245.124.37,1433;Initial
Catalog=myDatabaseName;User
ID=myUsername;Password=myPassword"
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ADO .NET
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Connection(2)

Managing Database Connections

DB connection represent a critical expensive and limited resource.

Connection Pooling

Open connections late and close them early
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ADO .NET
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Connection Pooling

Connection Pooling




Database connection pooling enables an application to reuse an
existing connection from a pool, instead of repeatedly establishing a
new connection with the database.
ADO .NET data providers provide transparent connection pooling,
the exact mechanics of which vary for each provider.
For example, using SQL Server .Net data provider you can configure
connection pooling by adding a name-value pairs to the connection
string: “[…];Max Pool Size=75; Min Pool Size=5”
Connections are pooled through an exact match algorithm on the
connection string!!! The pooling mechanism is even sensitive to
spaces between name-value pairs.
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ADO .NET
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Command

Command

This is the pipeline to the backend data.

The command object provides direct execution of the SQL
command to the database.

You can use the command to either ExecuteNonQuery(), which will
action an SQL statement (such as a DELETE command) upon the
data.

ExecuteReader() links straight in to the Data Reader object.
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Commands and Parameters

Commands and Parameters

When a SQL statement is executed, the database has to generate
an execution plan for it.

Use Prepare() method to generate and store an execution plan in
advance. The plan will be saved in the database cache so
subsequent statements will be executed much faster.

This method should be used only if the SQL statement will be
executed multiple times.

Use Parameter object, instead of hardcoding parameter values in a
SQL statement.
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Parameters - Example
string sConnString = "Server=(local);Database=Northwind;Integrated Security=True;";
string sSQL = "UPDATE Customers SET City=@sCity WHERE CustomerID=@sCustomerID";
SqlConnection oCn = new SqlConnection(sConnString))
SqlCommand oCmd = new SqlCommand(sSQL, oCn))
oCmd.CommandType = CommandType.Text;
oCmd.Parameters.Add("@sCustomerID", SqlDbType.NChar, 5);
oCmd.Parameters.Add("@sCity", SqlDbType.NVarChar, 15);
oCn.Open();
oCmd.Prepare(); // Prepare the execution plan
oCmd.Parameters["@sCustomerID"].Value = "ALFKI";
oCmd.Parameters["@sCity"].Value = “Jerusalem";
oCmd.ExecuteNonQuery();
oCmd.Parameters["@sCustomerID"].Value = "CHOPS";
oCmd.Parameters["@sCity"].Value = “Tel-Aviv";
oCmd.ExecuteNonQuery();
oCn.Close();
February 2nd, 2006
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Data Reader

Data Reader

This object essentially takes a stream of data from the Command
object and allows you to read it.

It's like a forward-only Recordset from the ADO and is very efficient
because it stores only one record in the memory at a time.

However this uses a server-side cursor, so you should avoid it too
much as it naturally requires an open connection.
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Data Adapter

Data Adapter

It essentially serves as a middle man, going through your connection
to retrieve data, then passing that into a DataSet.

You can then pass the DataSet back to the Data Adapter, which will
go and update the database.

The SQL statements for each command are specified in the
InsertCommand, UpdateCommand, SelectCommand and
DeleteCommand properties.
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DataSet
DataTable
DataSet
DataColumn
DataTable
DataRow
Relations
Constraints
XML Schema
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ADO .NET
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DataSet(2)

DataSet

The “king” of the ADO .NET

This object is actually a memory resident representation of data that
provides a consistent relational programming model regardless of the
data source.

The data stored in the DataSet object is disconnected from the
database!
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DataSet(3)

The DataSet object model is made up of three collections, Tables,
Relations and ExtendedProperties. These collections make up
the relational data structure of the DataSet

Tables Collection

Relations Collection

ExtendedProperties Collection
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ADO .NET
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DataSet(4)

Tables Collection




Relations Collection



DataSet.Tables
Each DataTable represents a table of data from the data source.
DataTable is made up of a Columns collection and a Rows collection.
DataSet.Relations
The DataRelation objects define a parent-child relationship between
two tables based on foreign key values.
ExtendedProperties Collection



DataSet.ExtendedProperties
The ExtendedProperties is a user-defined properties collection.
Can be used to store custom data related to the DataSet, such as the
time when the DataSet was constructed.
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ADO .NET
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DataSet(5)
DataSet
DataRelationCollection
ExtendedPropeties
DataTableCollection
DataTable
DataRowCollection
DataView
DataRow
ChildRelations
ParentRelations
Constraints
DataColumnCollection
ExtendedProperties
PrimaryKey
February 2nd, 2006
ADO .NET
DataColumn
ExtendedProperties
27
DataSet(6)

Connecting a DataSet to a data source


In order to connect a DataSet to a data source, we need to use the
DataAdapter as an intermediary between the DataSet and the .NET
data provider.
Let’s see some code…
February 2nd, 2006
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DataSet – Example

Filling the DataSet:
// Connection String
String conStr =
@"Provider=Microsoft.Jet.OLEDB.4.0;DataSource=C:\NWind.mdb";
//SQL Command
String sqlStr = "SELECT EmployeeID, FirstName, LastName FROM
Employees";
// Create a new DataAdapter object
OleDbDataAdapter da = new OleDbDataAdapter(sqlStr, conStr);
// Create a new DataSet
DataSet ds = new DataSet();
// Fill the DataSet
da.Fill(ds, "Employees");
February 2nd, 2006
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Transactions

Why do we need transactions?

Consider a Web-based retail application that processes purchase
orders. Each order requires three distinct operations that involve
three database updates:




The inventory level must be reduced by the quantity ordered.
The customer’s credit level must debited by the purchase amount.
A new order must be added to the orders database.
It is essential that these three distinct operations be performed as a
unit and in atomic fashion.
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Transactions(3)

Performing Manual Transactions with ADO .NET

ADO .NET supports a transaction object that you can use to begin a
new transaction and then explicitly control whether it should be
committed or rolled back.

The transaction object is associated with a single database
connection and obtained by the BeginTransaction() method of the
connection object.

You must explicitly associate each command objects with the
transaction by setting the Transaction property.

Note that since a transaction object associated with a single
connection you can perform transactions only with a single database.
February 2nd, 2006
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Transactions – Example

Transaction Example
SqlConnection db = new SqlConnection(conStr);
SqlTransaction transaction;
db.Open();
transaction = db.BeginTransaction();
try
{
new SqlCommand("INSERT INTO TransactionDemo(Text) VALUES ('Row1')", db,
transaction).ExecuteNonQuery();
new SqlCommand("INSERT INTO TransactionDemo(Text) VALUES ('Row2');",db,
transaction).ExecuteNonQuery();
new SqlCommand("INSERT INTO CrashMeNow VALUES ('Die', 'Die', 'Die');", db,
transaction).ExecuteNonQuery();
transaction.Commit();
}
catch (SqlException sqlError)
{
transaction.Rollback();
}
db.Close();
February 2nd, 2006
ADO .NET
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ADO .NET and XML

XML and Traditional Data Access

We have talked about data access as it relates to traditional data
access and relational data.

A wide variety of data can be represented in a non relational way.

ADO .NET makes it extremely easy to create and read XML
documents.

The data in ADO.NET is transported in XML format.

You can parse XML in .NET programmatically using the
System.Xml.XmlDataDocument object.
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ADO .NET and XML (2)

Saving DataSet as XML



Fill the DataSet with data.
Use DataSet.WriteXml(fileName) to write an XML file.
Loading XML files



Loading the XML file is not more complex than writing it.
Use DataSet.ReadXml(fileName) to load the data.
Wrap ReadXml call with try and catch because we can’t guarantee
that the file contains valid XML.
February 2nd, 2006
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ADO .NET and XML (3)

Schemas

Schemas provide a mechanism for defining rules that XML
documents must adhere to, and which help everyone understand
what the data held in an XML document actually is.

Generating a Schema


Fill the dataset
DataSet.WriteXmlSchema(SchemaFileName);
February 2nd, 2006
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ADO .NET and XML (4)
February 2nd, 2006
ADO .NET
36
ADO .NET and XML (5)

Typed DataSets





Typed DataSets can provide a more intuitive mechanism for the
manipulation of data.
A typed DataSet is early bound to an XML Schema Definition (XSD)
file.
Schemas provide very rigorous definitions for the types of particular
objects. In conjunction with the typed DataSet, they can allow access
to the tables and columns of a DataSet using meaningful names.
This not only improves the readability of the code
Enables Visual Studio .NET's IntelliSense feature to make contextsensitive suggestions as you type in code.
February 2nd, 2006
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Data Providers Diagram
Unmanaged
App
.NET Managed App
OLE DB .Net Data Provider
ADO
DataSet
OleDbConnection OleDbDataAdapter
OleDbCommand OleDbDataReader
Data Table
COM InterOp
SQL Server/Oracle
.Net Data Provider
OLE DB
Connection
DataAdapter
Command
DataReader
SQLOLEDB
Misc DB
February 2nd, 2006
SQL Server 6.5 and earlier
ADO .NET
SQL Server 7.0 and later
/ Oracle
38
Data Providers in the .NET
Framework

SqlClient Provider



(1)
Should be used to access SQL Server 7.0 or later, and MSDE
databases.
Can't be used with SQL Server 6.5 or earlier.
OleDb Provider


Good for almost anything other than SQL Server 7.0 or later,
or Oracle.
Using the ODBC data access through the OleDb is
discouraged – think of the architecture involved:
 ADO.NET – COM interop – (optional) OLE DB services –
OLE DB provider – ODBC driver – data source!
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Data Providers in the .NET
Framework

The Odbc Provider


(2)
Should be used whenever you need to access a data source
with no direct or OLE DB provider (PostgreSQL, Paradox,
dBase…),
OracleClient Provider


Supports Oracle data types, as well as ref cursors
Avoids the cost of COM interop, and also employs Oraclespecific optimizations
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Generic Interfaces


ADO.NET was designed from the beginning to allow the provider
writer the space to support database-specific features.
Programmers who wish to build applications that interact with
databases of more than one brand may resort to the generic
interfaces:








IDbConnection
IDbCommand
IDataReader
IDbTransaction
IDbDataParameter
IDataParameterCollection
IDbDataAdapter
There are problems involved with a common interface instead of
a common base class.

This issue will be covered in more depth in the slides about ado.net
2.0
February 2nd, 2006
ADO .NET
41
ADO.NET 2.0 Added Features

ADO.NET 2.0 comes with a plethora of new features.
We shall cover the main features in short:





Based-Class-Based Provider Model
Provider Factories
Asynchronous Commands
SqlDependency
MARS (Multiple Active Resultsets)
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ADO.NET 2.0 Added Features

Based-Class-Based Provider Model


In ADO.NET 1.X provider writers implemented a series of
provider-specific classes. Generic coding was based on the
generic interface each of the classes implemented.
The new provider model in ADO.NET 2.0 is based on a series
of base classes.


(1)
Each of the base classes implements the still-required generic
interface for backward compatibility.
Provider Factories

The base ProviderFactory class (DbProviderFactory) and the
ProviderFactories class
(System.Data.Common.ProviderFactories) simplify things a
bit…
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ADO.NET 2.0 Added Features

(2)
Conditional code that used to be written like this:

enum provider {sqlserver, oracle, oledb, odbc};
// determine provider from configuration provider
prov = GetProviderFromConfigFile();
IDbConnection conn = null;
switch (prov) {
case provider.sqlserver:
conn = new SqlConnection(); break;
case provider.oracle:
conn = new OracleConnection(); break;
case provider.oledb:
conn = new OleDbConnection(); break;
case provider.odbc:
conn = new OdbcConnection(); break;
// add new providers as the application supports them …
}
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ADO.NET 2.0 Added Features

(3)
...Can now be written like this:

// get ProviderInvariantString from configuration string
provstring = GetProviderInvariantString();
DbProviderFactory fact =
DbProviderFactories.GetFactory(provstring);
IDbConnection = fact.CreateConnection();
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ADO.NET 2.0 Added Features

Asynchronous Commands



(4)
database command execution can take a long time.
ADO.NET 2.0 SqlClient now provides built-in SqlCommand
methods that provide asynchronous execution.
SqlDependency

Caching is good. But we should make sure it’s consistent with
the database.
 Until now, this task was accomplished through triggers that
updated a file upon update of the database, or by
refreshing the cache every so often.
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ADO.NET 2.0 Added Features

(5)
SqlDependency contacts you when the underlying rows
change.



When notified, the entire set of rows is fetched again.
This functionality is good for a single cache or a limited set of
users.
However, when using it with large numbers of users listening at
the same time - the SELECT statements used for refresh could
be a significant hit on the database.
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ADO.NET 2.0 Added Features

(6)
MARS (Multiple Active Resultsets)

SQL Server doesn't automatically produce a cursor. Instead, it
uses an optimized method to pull the data in packet-size
chunks.

In the versions prior to SQL Server 2005, there could only be
one cursorless resultset active on a connection at a time.


ADO.NET 1.X throw an error if you attempt to open a second
cursorless resultset.
ADO "classic" actually opened a new database connection
behind the scenes.
 This convenience feature was inadvertently abused by some
programmers and resulted in more database connections
than they bargained for.
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48
ADO.NET 2.0 Added Features

(7)
MARS (contd)

In SQL Server 2005, the database has been
enhanced to permit MARS.
 Each SqlCommand can accommodate a
SqlDataReader, and multiple SqlDataReaders
can be used in tandem.
 It’s not just about reducing errors. It can be
extremely useful in conjunction with
asynchronous operations described above.

February 2nd, 2006
Example: Filling 20 drop-down list boxes on a form at
the same time, using a single connection.
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Summary: Pros & Cons

Pros






Performance
Managed Classes
XML Support (and Reliance)
Disconnected Operation Model
Rich Object Model
Cons



Managed-Only Access
Only four Managed Data Providers (so far)
Learning Curve
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Installation
Installation

Installing .Net Framework 1.1 is free



Getting Visual Studio 2003 is not free

http://msdn.microsoft.com/vstudio/Previous/2003/

There is VS Academic “only” for $99
Installing SQL Server 2000


http://msdn.microsoft.com/netframework/downloads/framework1_1/
http://www.microsoft.com/technet/prodtechnol/sql/2000/downloads/
NEXT->NEXT->… -> FINISH
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It’s DEMO Time
Remote DB Access Through
DataSet - Demo
Overview
DataSet
Web Service
Web Page
Data Provider
HTTP
SQL Server
Client
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