writing code to write your data services layer andrew novick december 6, 2001

Writing code to write your Data Services Layer

Andrew Novick

December 6, 2001

Andrew Novick [email protected] December 6, 2001 VB Pro User Group

Agenda

The Task: Creating a Data Services Layer Stored Procedure Based DSL Writing the code that writes the code Getting Metadata from SQL Server


Task: Create a Data Services Layer Write a Data Services Layer for a medium

to large database that is rapidly evolving

Use the fastest possible ADO techniques


The N-Tier Model

UserInterface

Layer

BusinessLayer

DataServices

Layer

Database


Data Services Layer

Responsible for all I/O with database Holds all the SQL Uses Stored Procedures for routine:

Insert Update Delete Select by Key


Why Stored Procedures for I/O

Reduced round-trips to the database. About 1/4th the trips used by ADO Recordsets

Reduced client CPU and Memory


Resource

ADO Examples and Best Practices William R. Vaughn

Apress ISBN 1-893115-16-X


Alternative ways of getting there

Buy a product Lockwood Tech – ProcBlaster OM Tool Carl Franklin’s Code

Build VBPJ Article


VBPJ June 2001Automate Writing Stored Procedures

Use SQL Server's Distributed Management Objects to generate standardized stored procedures. by David Rabb

URL: http://www.devx.com/premier/mgznarch/vbpj/2001/06jun01/dd0106/dd0601.aspTry not to give your users direct access to your database tables—they can poke around in your database and cause all kinds of trouble. Microsoft SQL Server provides one of the best methods for isolating users from your tables: stored procedures. However, unless you own a middle-tier database-modeling tool, you've probably been building and maintaining your stored procedures by hand. I'll show you how to use the metadata stored in SQL Server to create and maintain a set of standardized stored procedures for any SQL Server database (see Figure 1).

In this column's sample project, I'll show you how to create four procedures for each user table in the Pubs database: Select, Insert, Update, and Delete (download the code project). Select contains one parameter for each member of the table's primary key, and a select statement. It returns all columns for a single row in the table.

URL: http://www.devx.com/premier/mgznarch/vbpj/2001/06jun01/dd0106/dd0601.asp

http://www.devx.com/premier/mgznarch/vbpj/2001/06jun01/dd0106/dd0601.asp


http://www.devx.com/free/mgznarch/vbpj/code/2001/06jun01/vb0106dd.zip


http://www.vbpj.com/


Why Build

Total control Interfaces the way you want them Naming Conventions the way you want them. Error handling the way you want it.

Products require extensive customization and “script” writing. Might as well write it in VB


Using Stored Procedures for IUSD

Insert Update Select Delete


Sample Stored Procedure

CREATE PROCEDURE [dp_titles_ins]

@title_id varchar(6),

@title varchar(80),

@Booktype char(12) = NULL OUTPUT ,

@pub_id char(4) = NULL ,

@price money = NULL ,

@advance money = NULL ,

@royalty int = NULL ,

@ytd_sales int = NULL ,

@Booknotes varchar(200) = NULL ,

@pubdate datetime = NULL OUTPUT

AS


Sample Stored Procedure 2IF @Booktype Is Null

SET @Booktype = ('UNDECIDED')

IF @pubdate Is Null

SET @pubdate = (getdate())

INSERT INTO [titles] WITH (ROWLOCK) (

[title_id], [title], [Booktype], [pub_id], [price],

[advance], [royalty], [ytd_sales], [Booknotes],[pubdate])

Values (@title_id, @title, @Booktype, @pub_id, @price, @advance,

@royalty, @ytd_sales, @Booknotes, @pubdate)

SELECT @Booktype = [Booktype], @pubdate = [pubdate]

FROM [titles]

WHERE [title_id] = @title_id


What do the VB Classes Look Like?

To long to print here….

Multiple interfaces to the data.


Some Caveats

Naming convention for SQL Objects required 30 characters name limit No spaces in names No use of VB Reserved words Special Filed


What sort of Interface would you like?

Properties Compact Load, Add, Update Irec Browse


Property based Interface

Property Get and Let pairs for each variable

oTable.Field1 = ‘a new value’ oTable.Field1 = “another value’ ….. oTable.Update


Compact Functions

Load, Add, Update send all properties. Best when method calls cross machine or

context boundaries.

oTable.Add (my field1val, myField2Val myField3Val…..)


IRec Interface

Generic, works with all tables.

Dim oMyTable as cMyTableDim oRec as IRecSet oRec = oMyTablenFieldIndex = oRec.FieldIdx(“Name”)myVariable = oRec.FieldValue(nFieldIndex)


Browse

Writes the SQL to do standard browse access to tables.

Keeps SQL out of the UI and Business layers.


Take a look at Views

Similar to tables Usually not updateable


Classes Stored Procedures

3 Types of stored procedures Does not return a record set Returns a record set Returns an XML stream

Never updateable


Does not return a record set

oCMD.Execute RecordsAffected:=m_nRAd, Options:=adExecuteNoRecords


Returns XML

With oCMD

.Dialect = "{5D531CB2-E6ED-11D2-B252-00C04F681B71}"

Set .CommandStream = oStream

.Properties("Output Stream") = oResultStream

.Execute , , adExecuteStream

m_sXML = oResultStream.ReadText()

End With


5 Minutes

This is the true power of having a custom application

Would work even better as a VB Add-In


Alternatives for getting Schema Information

SQL-DMO ADOX INFORMATION-SCHEMAs


Real World Results

8000 Lines of Code in AppGenerator Writes 150,000 Lines of DSL Code

80 Hours vs. about 400 Hours

Change in effort level takes away an important disincentive for using stored procedures.

writing code to write your data services layer andrew novick december 6, 2001

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