Download Coding Standards

Object Relational Mapping
(ORM)
Persistence
• Almost all applications require some form of persistence.
• Almost all persistence is done using relational
databases.
• Usually the business classes are the ones that are
persisted.
Actual Example
lsSqlStatement = "INSERT INTO tblClaimsHistory " +
"(fldBatchLet, fldBatchNum, fldBatchFy,fldBatchReqSeq,
fldPatientSSN,fldProvTaxId,fldProvSuff,fldProvType,"+
"fldDiag1,fldDiag2,fldDiag3,fldDiag4, " +
"fldPatientLastName, fldPatientFirstName, fldProviderName ," +
"fldTotalCharged,fldTotalToPay,fldTotalDue,fldTotalCalcAmount,fldTotalPaid,
"+
"fldRecDate, fldClaimBeginDate,
fldClaimEndDate,fldCurrDocNum, fldMailCode, MessageIdentifier ) " +
"VALUES
('"+lsBatchNum.Substring(0,1)+"',"+lsBatchNum.Substring(1)+","+lsBatchFy+",'"+
lsBatchReqSeq + "', '" +lsSSN+"','"+lsFedTaxID+"','"+lsProvTaxSfx+"','"+
lsProviderType +"','"+ fldDiag1+"','"+fldDiag2+"','"+fldDiag3+"','"+fldDiag4
+fldPatientLastName+"','"+fldPatientFirstName+"','" +lsProviderName+"',"+
fldTotalCharged+","+fldTotalToPay+","+fldTotalDue+","+fldTotalCalcAmount+",
"+fldTotalAmtPaid +",'"+ ClaimRecievedDate + "','" + fldClaimBeginDate + "','" +
fldClaimEndDate + "','"+fldCurrDocNum+"','"+fldMailCode+"','"+MessageIdentifier+"') "
+"SELECT @@IDENTITY AS 'Identity'";
And as preparation we need:
lsBeginDate = lsBeginDate.Replace("-", "/");
lsEndDate = lsEndDate.Replace("-", "/");
OR
Replace("'","''");
Usually we have
• A business Object
• & A database Table
Customer
Customer
-ID
-Name
-Description
-Address
ID
Name
Desciption
Addresss
Traditional way to handle persistence
–
–
–
–
UI Tier
Business Tier
Data Tier
Database
UI tier
Business tier
Data Tier
Data
base
• Using a N-Tier design
This approach requires
• Long and tedious work to:
– Build SQL statements for Insert, update, Delete,
select
– Send the Objects’ properties to the data layer as
parameters
– Account for different types of databases/data fields
(ex: ‘ ‘ for strings and dates, format dates, handling
Null values,..
– Handle IDs, Keys,..
This work is usually..
•
•
•
•
Time Consuming
Boring
Error Prone
And most importantly:
– Doesn’t require much thinking
– Shifts focus from main target ( handle business case)
ORM
• ORM is about Mapping an Object to one or more
database tables.
• It eliminates the need to create a data layer tier ( data
layer is implicit)
• “In a nutshell, object/relational mapping is the automated
(and transparent) persistence of objects in an application
to the tables in a relational database, using metadata
that describes the mapping between the objects and the
database.”
• In short: ORM saves you from writing boring and error
prone code thus saving time and getting better quality.
Main Advantages of ORM
•
•
•
•
Better productivity ( no more tedious coding)
Better performance
DB independence
Less error prone
Many ORM tools, Many Approaches
• There are different Tools for implementing ORM using
different approach
– Using Attributes in the classes (GENTLE.NET)
– Using XML mapping Files (NHIBERNATE)
– Using Visual Mapping,
– … etc.
Introduction to GENTLE.NET
•
•
•
•
•
•
•
•
Open source, free tool.
Supports many DB types.
Uses attributes .. No complex configuration files
Queries generated at runtime using features in the .NET
framework (class attributes)
Handles “impedance mismatch” (Null values, auto
generated keys,..)
Handles transactions
Supports caching
Supports validations on the object level
Example Class
public class User
{
private int userId;
private string userName;
public User( int userId, string userName
)
{
this.userId = userId;
this.userName = userName;
}
public int Id
{
get{ return userId; }
set{ userId = value; }
}
public string Name
{
get{ return userName; }
set{ userName = value; }
}
}
• To be saved in
User
ID
Name
All we need to do is
1. Add reference to 3 DLLs
2. Add 3 “using..” lines
3. Add appropriate attributes to object
propertied
Class Becomes
using Gentle.Framework;
[TableName("Users")]
public class User : Persistent
{
private int userId;
private string userName;
// this is used by clients to construct new users
public User( string userName ) : this( 0, userName ) {}
// this is used by Gentle to reconstruct objects read from the database
public User( int userId, string userName )
{
this.userId = userId;
this.userName = userName;
}
// this is used by client to fetch users from the database
static public User Retrieve( int userId )
{
Key key = new Key( typeof(User), true, "Id", userId );
return Broker.RetrieveInstance( typeof(User), key ) as User;
}
[TableColumn("UserId"), PrimaryKey(AutoGenerated=true)]
public int Id
{
get{ return userId; }
set{ userId = value; }
}
[TableColumn(NotNull=true)]
public string Name
{
get{ return userName; }
set{ userName = value; }
}
}
• That was all the “SQL” we need to write.
• Also we don’t need to “create” an object
from a row in DB. It is done implicitly
• To save an object all we need to do is:
User ford = new User( "Ford Prefect" );
ford.Persist();
• To Load an object all we need to do is:
User prefect = User.Retrieve( ford.Id );
Using Id ( or any other Key)
BINGO !!!
Demo
Additives
Using SQL builder
static public IList ListByNameStartsWith( string partialName )
{
SqlBuilder sb = new SqlBuilder( StatementType.Select, typeof(User) );
// note: the partialName parameter must also contain the %'s for the LIKE query!
sb.AddConstraint( Operator.Like, "Name", partialName );
// passing true indicates that we'd like a list of elements, i.e. that no primary key
// constraints from the type being retrieved should be added to the statement
SqlStatement stmt = sb.GetStatement( true );
// execute the statement/query and create a collection of User instances from the
result set
return ObjectFactory.GetCollection( typeof(User), stmt.Execute() );
}
Additives
• Retrieving Lists of objects
• IList is directly bindable with data grids.
GentleList list = new GentleList(
typeof(User), parentInstance );
Additives
• Generating business class using
MyGeneration
– Demo
References
• http://www.mertner.com/projects/gentle
• http://www.mygenerationsoftware.com
Thank You!
Emad Magdy