Download Interfacing possibilities in Microsoft Access, using external data

Papers of the Sibiu Alma Mater University Conference, Fifth Edition, 24–26 March 2011, Sibiu – Volume 1
Interfacing possibilities in Microsoft Access, using external data sources
and Visual Basic for Application code sequences
Ilie ŞUFANĂ
Sibiu Alma Mater University, 57 Somesului St., 550003 Sibiu, Romania
Tel. / Fax: +40 0269 250008, e-mail: [email protected]
Abstract
This article presents a few possibilities of interfacing provided by Microsoft Access, containing
information coming from other sources, also knowing the fact that Microsoft Access allows using
many types of data from other data bases: table computing sheets, text files or by means of these being
copied or linked to these data.
Keywords: Microsoft Access, Microsoft SQL Server, Queries, Forms, Reports, Macrocommands,
Modules.
Rezumat
Acest articol prezintă câteva posibilităţi de interfaţare oferite de Microsoft Access, conţinând
informaţii provenite din alte surse, ştiind că Microsoft Access permite folosirea mai multor tipuri de
date din alte baze de date: foi de calcul tabelare, fişiere text sau prin copierea acestora sau relaţionarea
lor la aceste date.
Cuvinte-cheie: Microsoft Access, Microsoft SQL Server, Interogări, Formulare, Rapoarte,
Macrocomenzi, Module
1. Introduction
Microsft Acess provides the interfacing possibility
using data stored outside the current database. It
can be data from another Microsoft Access
database as well as data stored in different files,
including files from Foxpro, dBase, Paradox,
Lotus, Excel and others.
Access is an excelent product which provides
powerfull and efficient methods for data
presentation, including external data.
Access data is stored in external files due to
different reasons. For example, large databases can
be administrated more efficiently on a back-end
database server like Microsoft SQL SERVER.
Frequently, data is stored in Foxpro, dBase or
Paradox files because it is used by older
applications written in this programming
languages. Access data can be stored in other
databases, different from the one from your
application. No matter how the data is stored, it is
necessary to understand how to use this data using
the user interface, as well as how to manipulate
external data using VBA modules. Therefore we
can access data from other sources, we can create
interrogations, forms and reports using this data.
2. Discussion
2.1. Creating the interface using external data
For accessing external data we have two
possibilities. We can access the data by creating a
link from our Access database or we can directly
open a data source. Whenever it is possible we
would like to create a link with external files. By
doing so we will increase the performance of the
the external data manipulation process.
2.2. Creating a link with an external table
Links with external data can be easily created
using front-end instruments provided by Access.
For creating a link with a table from another
Access database or from any other database, right
click on one of the database label and then select
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Ilie ŞUFANĂ - Interfacing possibilities in Microsoft Access, using external data sources and VBA code sequences
the Link Tables option or the Get External Data
(receives external data) from the File tab and then
choose Link Tables. From the dialog box which
will appear on the screen, select the name and the
type of the file with ehich you want to link. After
selecting a file and after you fill the required
information, you have to click on the Link button.
A Link Tables dialog box will appear which allows
you to select the table with which you wish to
create a link. After selecting the table and after
pressing OK, the table you selected will appear on
the screen, among the other tables from your
database. You can create queries, forms, reports,
macro commands and modules which will work
with your attached table.
You can modify only certain properties of the
table. You cannot change the structure of the table
you attached. For example, you cannot change the
type or length of a field. But you can add a title to
a certain field. If you try to modify the table’s
structure, a dialog box will appear and by clicking
„Yes” in the dialog box you are permitted to
change only certain properties of the attached
table. However, after you visualize the table in the
Design mode, Access informes you on the
properties you can and cannot modify. Every
property that cannot be modified has the „This
property cannot be modified in linked tables”.
For creating a link with an external table, using
VBA instructions, you need to follow four steps:
a) Open your Microsoft Access database, which
will contain the link with the external table
b) Create a new table definition using the external
data source.
c) Set the configuration values for the external
database and for the external table.
d) Link the table to the database by adding the
table definition.
Here is an example of the four steps, using VBA
instructions:
Sub
ConnectToFox(sDirName
As
String,
sTableName As String, sAccessTable)
Dim db As Database
Dim td As TableDef
Set db = CurrentDb
Set td = td.CreateTableDef(sAccessTable)
td.Conect = “FoxPro 2.6;DATABASE=“ &
sDirName
td.SourceTableName = sTableName
db.TableDefs.Append td
End Sub
The subroutine can be called in the following way:
Call ConnectToFox (“C:\Fpw26\Tutorial” ,
“customer” ,”tblCustomer” )
The ConnectToFox subroutine, receives three
parameters when it is called. The first one is the
name of the folder in which FoxPro is stored. The
second one is the name of the file with which you
wish to link, without the DBF extension. And the
third parameter is the name of the table you which
to create. The subroutine creates two object
variables. The first one is of database type and the
second one is of table definition type. After this, it
sends the database type object to the current
database and after that it creates a table definition
with the name tblCustomer. For this table
definition it creates a connection string. The string
specified in the subroutine indicates that you will
create a link with a FoxPro 2.6 table. The name of
the folder acts the same as the database with which
you want to link. After configuring the definition
table’s Connect property, you are ready to insert
the name of the table with which you want to
create a link. This is the name of the FoxPro file.
In the end you are ready to add the table definition
to your own database.
For creating a link with an Access table, stored in
an other database, the following subroutine will be
called:
Sub ConnectToAccess(sDBName As String,
sTableName As String, sAccessTable)
Dim db As Database
Dim td As TableDef
Set db = CurrentDb
Set td = td.CreateTableDef(sAccessTable)
td.Conect = “;DATABASE=“ & sDBName
td.SourceTableName = sTableName
db.TableDefs.Append td
End Sub
It can be seen that the database with which you are
trying to connect isn’t specified. All the other
operations from the subroutine are identical with
the ones from the FoxPro file connection
subroutine.
2.3. Opening an external table
It is always more convenient to create a link to a
table instead of opening an external table. This is
due to the supplementary performance of the link
method, and also due to the fact that it is very easy
to use a linked table. After you created a link with
a table, you can treat it as any other Access table.
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Papers of the Sibiu Alma Mater University Conference, Fifth Edition, 24–26 March 2011, Sibiu – Volume 1
However there are some cases that require you to
open an external table without creating a link.
For opening an external table you must follow two
steps:
a) Opening the database using the OpenDatabase
method.
b) Creating an Recordset type object based on the
external table.
Here is how this kind of program looks like:
Sub OpenExternal(sDBName As String,
sTableName As String)
Dim db As Database
Dim rs As Recordset
Set db =
DBEngine.Workspace(0).OpenDatabase(sDBNam
e)
Set rs = db.OpenRecordset(sTableName)
Do While Not rs.EOF
Msgbox rs.Field (0).Value
rs.MoveNext
Loop
End Sub
Call OpenExternal
(“C:\access\facturi.mdb”,”Facturi”)
– In Access, views are called queries. As for SQL
Server, one can create queries that can be
modified, select lines from a query and create
associations between several tables which are
represented as queries
– In SQL Server, columns represent data
elements from a line. Although the term ‘line’
keeps its meaning in Access, the columns are
called fields
– The data types don’t have the same name and,
in many cases, they physically differ when
talking about SQL Server and Access. There
are also other differences, but these are the
main differences that may come in handy when
using SQL Server together with Access. If you
have an Access application, this is composed of
up to six different elements. A short
explanation of these elements is presented next,
the extent to which these elements will be
exposed to migration or conversion to SQL
Server also being presented.
2.5. Tables
You can see that in this case you don’t add a table
definition. Instead of adding a table definition, you
create a temporary Recordset which refers to the
external data. After opening the external table as a
Recordset, you will go through every record of the
table, with displaying the value from the first field.
Once you’ve opened the Recordset you can use it
as you wish.
2.4. Using Microsoft Access together
with SQL Server
Microsoft Access represents an excellent
development environment, with many of the SQL
Server facilities available for testing and planning
the implementation. Due to the fact that Access is a
more reduced engine and because it has no real
client/server operation, its use as a server system in
a larger implementation is limited. However, it still
remains an unique development environment when
talking about database handling.
Access provides a good user interface for
developing tables and relations. There is a series of
differences in the way that Access handles
databases, including the issue of physical storage,
and the specific terminology is slightly different.
Here are a few examples:
Similar to SQL Server. This is probably the the
most important element that will experience
migration. Tables in Access contain the lines of
information that will be converted to SQL Server.
2.6. Queries
Queries will probably require a conversion, which
will have to be done mostly manually. So the SQL
code which is behind every query will have to be
examined and the corresponding SQL Server views
will be created. Let’s also keep in mind that a
connection to a SQL Server view can be created
and used in a similar way to a table.
2.7. Forms
Forms are not converted to SQL Server. Let’s
recall that in the client/server model, the client
system is in charge of handling the user interface
and the server is in charge of maintaining and
manipulating data.
2.8. Reports
Like in the case of forms, reports aren’t usually
converted. However, query based reports are
different. In Access, a query can be created inside
of a report. In order to obtain the best result, it is
good to examine the properties catalogue of each
report and to create SQL Server views based on the
queries that were found. Then the queries from the
report can be replaced by the new views. The
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Ilie ŞUFANĂ - Interfacing possibilities in Microsoft Access, using external data sources and VBA code sequences
performance will be better, the reports will act as if
the query is created inside of them, but the
effective result is a client/server implementation of
the report.
2.9. Macrocommands
Macrcommands are elements that are exclusively
specific to the Access environment. It is possible
that the macrocommands could call queries or
execute commands at a higher level, so that an
examination could be in order. Like in the case of
reports, it is not recommended to use query based
macrocommands, because these queries can be
placed in SQL Server with a better performance.
sub-routine has to be examined in order to
determine how the migration should be done. In
the case of modules, we have several options. We
can transform a sub-routine in a stored procedure,
in a view or in a dynamic query. This all depends
on the processing that is done inside the database.
The modifications will be done in short sequences,
while continuously testing. It is very important to
rigorously check the changes that were made
before going to the next conversion, because the
basic functionality of the system is involved.
References
2.10. Modules
Viescas J.L. 1999. Totul despre Microsoft Access 97,
Editura Teora, Bucureşti.
Modules can be rarely automatically exposed to
migration. This means that each procedure and
Morgan B. & Perkins J. 1997. SQL fără profesor în 14
zile, Editura Teora, Bucureşti.
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