This article discusses Recital database security: from operating system file permissions through file and field protection to DES3 encryption.

Overview

A company's data is extremely valuable and must be protected, both in operation and in physical file format. Recital products provide a range of ways to protect your data.

Operating System File Permissions

The most basic level of database security is provided by the operating system. Recital database tables and indexes are individual files with their own respective operating system file permissions. Read permission is required to open a table and write permission to update a table. If a user does not have read permission they are denied access. Without write permission, a table will be opened read-only.

Here the owner, root, and members of the recital group have write permission, so can update the example table unless additional protection applies. Other users can only open the example table read-only.

# ls -l example*
-rwxrwxr-x    1 root     recital       147 Nov 29 14:27 example.dbd
-rwxrwxr-x    1 root     recital     41580 Nov 29 14:27 example.dbf
-rwxrwxr-x    1 root     recital     13312 Nov 29 14:28 example.dbt
-rwxrwxr-x    1 root     recital     19456 Nov 29 14:28 example.dbx

Note: As in the example above, a table's associated files should have the same permissions as the table itself:

File Extension	File Type
.dbd	Dictionary
.dbf	Table
.dbt	Memo
.dbx	Index

Database Dictionary

Each Recital table may have a Database Dictionary. The Dictionary can be used both to protect the integrity of the data and to protect access to the data. This section covers Column Constraints, Triggers, Security and Protection.

Column Constraints: Data Integrity

The Dictionary attributes or constraints either prevent the entry of incorrect data, e.g. must_enter and validation or aid the entry of correct data, e.g. default, picture and choicelist. The Dictionary can be modified in the character mode CREATE/MODIFY STRUCTURE worksurface, via SQL statements, or in the Recital Enterprise Studio Database Administrator.

Click image to display full size

Fig 1: MODIFY STRUCTURE Worksurface: Dictionary.

The SQL Column Constraints are as follows:

Constraint	Description
AUTO_INCREMENT | AUTOINC	Used to auto increment the value of a column.
CALCULATED	Used to calculate the value of a column.
CHECK | SET CHECK	Used to validate a change to the value of a column.
DEFAULT	Used to set a default value for the specified column.
DESCRIPTION	Used set the column description for the specified column.
ERROR	Used to define an error message to be displayed when a validation check fails.
FOREIGN KEY	Used to define a column as a Foreign Key for a parent table.
NOCPTRANS	Used to prevent code page translation for character and memo fields.
NOT NULL | NULL	Used to disallow/allow NULL values.
PRIMARY KEY	Used to define a table’s Primary Key.
RANGE	Used to specify minimum and maximum values for a date or numerical column.
RECALCULATE	Used to force recalculation of calculated columns when a column’s value changes.
REFERENCES	Used to create a relationship to an index key of another table.
UNIQUE	Used to define the column as a candidate index for the table

These can be specified in CREATE TABLE or ALTER TABLE statements:

exec sql
  OPEN DATABASE southwind;
exec sql
  ALTER TABLE customers ADD COLUMN timeref char(8) CHECK validtime(timeref)
  ERROR "Not a valid time string";

Click image to display full size

Fig 2: Database Administrator: Column Constraints and Attributes.

TRIGGERS

Table Level Triggers are event-driven procedures called before an I/O operation. These can be used to introduce another layer of checks before a particular operation is permitted to take place or to simply set up logging of those operations.

The CREATE/MODIFY STRUCTURE worksurface <TRIGGERS> menu bar option allows you to specify table level triggers. You may edit a trigger procedure from within the <TRIGGERS> menu by placing the cursor next to the procedure name and pressing the [HELP] key. A text window pops up for editing. If the table triggers are stored in separate <.prg> files, rather than in a procedure library, procedures need not be predefined (SET PROCEDURE) before using the table.

Click image to display full size

Fig 3: MODIFY STRUCTURE Worksurface: Triggers.

 

The following triggers can be selected and associated with a specified procedure name in the <TRIGGERS> menu.

Trigger	Description
UPDATE	The specified procedure is called prior to an update operation on the table. If the procedure returns .F., then the UPDATE is canceled.
DELETE	The specified procedure is called prior to a delete operation on the table. If the procedure returns .F., then the DELETE is canceled.
APPEND	The specified procedure is called prior to an append operation on the table. If the procedure returns .F., then the APPEND is canceled.
OPEN	The specified procedure is called after an open operation on the table.
CLOSE	The specified procedure is called prior to a close operation on the table.
ROLLBACK	The specified procedure is called when a user presses the [ABANDON] key in a forms based operation.

The Recital Enterprise Studio Database Administrator also allows you to associate existing programs as Table Trigger Procedures.

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Fig 4: Database Administrator: Triggers.

 

Programmatically, Trigger Procedures can also be associated with a table using SQL. The following table constraints may be applied in the SQL CREATE TABLE and ALTER TABLE statements:

Trigger	Description
ONUPDATE	The specified procedure is called prior to an update operation on the table. If the procedure returns .F., then the UPDATE is canceled. e.g. SQL> ALTER TABLE customer modify ONUPDATE "p_update";
ONDELETE	The specified procedure is called prior to a delete operation on the table. If the procedure returns .F., then the DELETE is canceled. e.g. SQL> ALTER TABLE customer modify ONDELETE "p_delete";
ONINSERT	The specified procedure is called prior to an insert operation on the table. If the procedure returns .F., then the INSERT is canceled. e.g. SQL> ALTER TABLE customer modify ONINSERT "p_insert";
ONOPEN	The specified procedure is called after an open operation on the table. e.g. SQL> ALTER TABLE customer modify ONOPEN "p_open";
ONCLOSE	The specified procedure is called prior to a close operation on the table. e.g. SQL> ALTER TABLE customer modify ONCLOSE "p_close";
ONROLLBACK	The specified procedure is called when a user presses the [ABANDON] key in a forms based operation. e.g. SQL> ALTER TABLE customer modify ONROLLBACK "p_rollback";

SECURITY

As mentioned above, all Recital files are subject to Operating System read and write permissions. These permissions can be further refined, while still using the Operating System user and group IDs, in the Security and Protection sections of the Dictionary. The Security section handles table based operations and the Protection section focuses on individual fields.

Security and Protection rules can be defined in the CREATE/MODIFY STRUCTURE worksurface of Recital Terminal Developer, via the SQL GRANT and REVOKE statements or in the Recital Enterprise Studio Database Administrator.

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Fig 5: MODIFY STRUCTURE Worksurface: Security.

 

The Security section has table operations for which Access Control Strings can be specified. An Access Control String (ACS) is a range of valid user identification codes, and is used to restrict table operations to certain individuals or groups. Each user on the system is allocated a group number and a user number. The user identification code is the combination of group and user numbers. When constructing an Access Control String of linked user identification codes, wild card characters may be used.

Example ACS	Description
[1,2]	In group 1, user 2
[100,*]	In group 100, all users
[2-7,*]	In groups 2-7, all users
[*,100-200]	In all groups, users 100-200
[1,*]&[2-7,1-7]	In group 1, all users, in groups 2-7, users 1-7

Please note that the maximum ACS length is 254 characters. OpenVMS group and user numbers are stored and specified in octal. On other Operating Systems, group and user numbers are stored and specified in decimal.

Access Control Strings may be associated with the following operations:

Operation	Description
READONLY	Users specified in the ACS have read-only access to the table. All other users have update access.
UPDATE	Users specified in the ACS have update access to the table. All other users are restricted to read-only access.
APPEND	Users specified in the ACS can append records into the table. No other users can append.
DELETE	Users specified in the ACS can delete records from the table. No other users can delete.
COPY	Users specified in the ACS can copy records from the table. No other users can copy.
ADMIN	Users specified in the ACS can use the following commands: SET DICTIONARY TO MODIFY STRUCTURE PACK ZAP REINDEX All other users cannot, except the creator of the table, who is always granted ADMIN access.

The corresponding SQL privileges are:

Operation	Description
SELECT	Users specified in the ACS may name any column in a SELECT statement. All other users have update access.
UPDATE	Users specified in the ACS may name any column in an UPDATE statement. All other users are restricted to read-only access.
INSERT	Users specified in the ACS can INSERT rows into the table. No other users can INSERT.
DELETE	Users specified in the ACS can DELETE rows from the table. No other users can DELETE.
ALTER	Users specified in the ACS can use the ALTER TABLE statement on this table.
READONLY	Users specified in the ACS may read any column in a SELECT statement. All other users have update access.

// Grant insert privilege for the customer table
exec sql
  OPEN DATABASE southwind;
exec sql
  GRANT UPDATE (lastname, firstname)
  INSERT ON customers
  TO '[20,100]'; 
	
// Grant all privileges to all users
exec sql
  OPEN DATABASE southwind;
exec sql
  GRANT ALL 
  ON shippers TO PUBLIC;

PROTECTION

Security and Protection rules can be defined in the CREATE/MODIFY STRUCTURE worksurface of Recital Terminal Developer, via the SQL GRANT and REVOKE statements or in the Recital Enterprise Studio Database Administrator.

Click image to display full size

Fig 6: Database Administrator: Protection.

 

The format of the ACS is the same as in <SECURITY> above. The following protection can be defined:

Operation	Description
READONLY	Users specified in the ACS have read-only access to the field. All other users have update access.
UPDATE	Users specified in the ACS have update access to the field. All other users are restricted to read-only access.

Recital Terminal Developer also has 'HIDDEN' Protection:

Operation	Description
HIDDEN	Users specified in the ACS see the 'hiddenfield'character rather than the data in the field. All other users see the data.

Hidden fields can be accessed and viewed on a work surface, but the field contains the hiddenfield character, ‘?’. If the field is referenced in an expression, it will contain the following: blanks for character fields, ‘F’ for logical fields, 00/00/0000 for date fields and blank for memo fields.

The corresponding SQL privileges are:

Operation	Description
SELECT	Users specified in the ACS may name the column in a SELECT statement. All other users have update access.
UPDATE	Users specified in the ACS may name the column in an UPDATE statement. All other users are restricted to read-only access.
READONLY	Users specified in the ACS may read the column in a SELECT statement. All other users have update access.

// Grant update privilege for columns lastname and firstname from the customer table
exec sql
  OPEN DATABASE southwind;
exec sql
  GRANT UPDATE (lastname, firstname)
  customers TO '[20,100]';

Encryption

From Recital 8.5 onwards, Recital installations that have the additional DES3 license option have the ability to encrypt the data held in Recital database tables. Once a database table has been encrypted, the data cannot be accessed unless the correct three-part encryption key is specified, providing additional security for sensitive data.

ENCRYPT

The ENCRYPT Recital 4GL command is used to encrypt the data in the specified table or tables matching a skeleton. If the skeleton syntax is used, then all matching tables will be given the same encryption key. The encryption key is a three part comma-separated key and may optionally be enclosed in angled brackets. Each part of the key can be a maximum of 8 characters. The key is DES3 encrypted and stored in a .dkf file with the same basename as the table. After encryption, the three parts of the key must be specified correctly before the table can be accessed.

// Encrypt individual tables
encrypt customers key "key_1,key_2,key_3"
encrypt employees key "<key_1,key_2,key_3>"

// Encrypt all .dbf files in the directory
encrypt *.dbf key "key_1,key_2,key_3"

SET ENCRYPTION

If a database table is encrypted, the correct three-part encryption key must be specified before the table's data or structure can be accessed. The SET ENCRYPTION TO set command can be used to specify a default encryption key to be used whenever an encrypted table is accessed without the key being specified. The encryption key is a three part comma-separated key.

If the command to access the table includes the key, either by appending it to the table filename specification or using an explicit clause, this will take precedence over the key defined by SET ENCRYPTION TO.

Issuing SET ENCRYPTION TO without a key causes any previous setting to be cleared. The key must then be specified for each individual encrypted table.

The default key defined by SET ENCRYPTION is only active when SET ENCRYPTION is ON. SET ENCRYPTION OFF can be used to temporarily disable the default key. The SET ENCRYPTION ON | OFF setting does not change the default key itself. SET ENCRYPTION is ON by default.

// Encrypt individual tables
encrypt customers key "key_1,key_2,key_3"
encrypt shippers key "key_2,key_3,key_4"
// Specify a default encryption key
set encryption to "key_1,key_2,key_3"
// Open customers table using the default encryption key
use customers
// Specify shippers table's encryption key
use shippers<key_2,key_3,key_4>
// Disable the default encryption key
set encryption to
// Specify the individual encryption keys
use customers encryption "key_1,key_2,key_3"
use shippers<key_2,key_3,key_4>

DECRYPT

The DECRYPT command is used to decrypt the data in the specified table or tables matching a skeleton. The specified key must contain the three part comma-separated key used to previously encrypt the table and may optionally be enclosed in angled brackets. The skeleton syntax can only be used if all tables matching the skeletonhave the same key.

The DECRYPT command decrypts the data and removes the table’s .dkf file. After decryption, the key need no longer be specified to gain access to the table.

// Decrypt individual tables
decrypt customers key "key_1,key_2,key_3"
decrypt employees key "<key_1,key_2,key_3>"

// Decrypt all .dbf files in the directory
decrypt *.dbf key "key_1,key_2,key_3"

All of the following commands are affected when a table is encrypted:

• APPEND FROM
• COPY FILE
• COPY STRUCTURE
• COPY TO
• DIR
• USE
• SQL INSERT
• SQL SELECT
• SQL UPDATE

APPEND FROM

Used to append records to the active table from another table.

// The key must be specified for an encrypted source table
use mycustomers
append from customers encryption "key_1,key_2,key_3";
for country = "UK"

COPY FILE

Used to copy a file.

// The key file must also be copied for an encrypted source table
// as the target table will be encrypted
encrypt customers key "key_1,key_2,key_3"
copy file customers.dbf to newcustomers.dbf
copy file customers.dkf to newcustomers.dkf
use newcustomers encryption "key_1,key_2,key_3"

COPY STRUCTURE

Used to copy a table's structure to a new table.

// The key file is automatically copied for an encrypted source table
// and the target table encrypted
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy structure to blankcust
use blankcust encryption "key_1,key_2,key_3"

COPY TO

Used to copy a table.

// By default, the key file is automatically copied for an encrypted
// source table and the target table encrypted with the same key
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy to newcustomers
use newcustomers encryption "key_1,key_2,key_3"

// You can also create a copy with a different key
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy to newcustomers encrypt "newkey_1,newkey_2,newkey_3"
use newcustomers encryption "newkey_1,newkey_2,newkey_3"

// Or create a decrypted copy
encrypt customers key "key_1,key_2,key_3"
use customers encryption "key_1,key_2,key_3"
copy to newcustomers decrypt
use newcustomers

// You can also create an encrypted copy of a non-encrypted source table
use orders
copy to encorders encrypt "newkey_1,newkey_2,newkey_3"
use encorders encryption "newkey_1,newkey_2,newkey_3"

DIR

Used to display a directory listing of tables.

// Encrypted tables are flagged as such with (DES3)
> open database southwind
> dir

Current database: southwind
Tables				# Records		Last Update	Size		Dictionary	Triggers	Security
categories.dbf			8			01/10/06		24576	None		None		None
cisamdemo.dbf       ---> CISAM/Bridge        [cisamdemo]
customers.dbf (DES3)		91			05/12/04		49600	None		None		None
employees.dbf			9			05/12/04		25520	None		None		None
example.dbf   (DES3)		100			12/24/05		38080	Yes		Yes		None
order_details.dbf			2155			05/12/04		296320	None		None		None
orders.dbf				829			05/12/04		232704	None		None		None
products.dbf			77			05/12/04		37112	None		None		None
productsbyname.dbf		77			05/12/04		29104	None		None		None
shippers.dbf  (DES3)		3			05/12/04		20864	None		None		None
suppliers.dbf			29			12/08/05		29992	Yes		None		None

   0.765 MB in 11 files.
   1.093 GB remaining on drive.

USE

Used to open a table.

// The three part key must be specified to open an
// encrypted table.  All of the following are valid.
// 1. Specifying a default encryption key before opening the table
set encryption to "key_1,key_2,key_3"
use customers
// 2. Appending the key to the filename
use customers<key_1,key_2,key_3>
// 3. Using the ENCRYPTION clause, optionally specifying angled brackets
use customers encryption "key_1,key_2,key_3"
use customers encryption "<key_1,key_2,key_3>"

SQL INSERT

Used to add a row to a table via SQL.

// The three part key can be specified using a
// default encryption key before opening the table
exec sql
  OPEN DATABASE southwind;
exec sql
  SET ENCRYPTION TO "key_1,key_2,key_3";
exec sql
  INSERT INTO customers
  (customerid, companyname)
  VALUES
  ('RECIT','Recital Corporation');
// Or by appending the key to the filename
exec sql
  OPEN DATABASE southwind;
exec sql
  INSERT INTO customers<key_1,key_2,key_3>
  (customerid, companyname)
  VALUES
  ('RECIT','Recital Corporation');

SQL SELECT

Used to return data from a table via SQL.

// The three part key can be specified using a
// default encryption key before opening the table
exec sql
  OPEN DATABASE southwind;
exec sql
  SET ENCRYPTION TO "key_1,key_2,key_3";
exec sql
  SELECT * FROM customers;
// Or by appending the key to the filename
exec sql
  OPEN DATABASE southwind;
exec sql
  SELECT * FROM customers<key_1,key_2,key_3>;

SQL UPDATE

Used to update data in a table via SQL.

// The three part key can be specified using a
// default encryption key before opening the table
exec sql
  OPEN DATABASE southwind;
exec sql
  SET ENCRYPTION TO "key_1,key_2,key_3";
exec sql
  UPDATE customers
  SET companyname='Recital Corporation Inc.'
  WHERE customerid='RECIT';
// Or by appending the key to the filename
exec sql
  OPEN DATABASE southwind;
exec sql
  UPDATE customers<key_1,key_2,key_3>
  SET companyname='Recital Corporation Inc.'
  WHERE customerid='RECIT';

Summary

Recital offers a range of ways to keep your data secure. These start with the Operating System read/write permissions, which can be further refined to the level of table I/O operations and then field access in the Dictionary based Security and Protection rules. The Dictionary also provides the means to protect the integrity of the data via data validation and to assist in correct data entry through the use of choicelists, help messages and picture clauses etc. A further role of the Dictionary is in the provision of Table Triggers, which can be used to enable a programmatic response to table operations to add in additional checks or audit trails. For the most sensitive data, DES3 encryption is the ultimate protection: encrypting the physical data on the disk and only permitting table access on the production of the three part encryption key.

If when your attempt to create device meta-data fails this is drbd preventing you from corrupting a file system present on the target partition.

$ drbdadm create-md drbd0

v08 Magic number not found
md_offset 30005817344
al_offset 30005784576
bm_offset 30004867072

Found ext2 filesystem which uses 190804004 kB
current configuration leaves usable 29301628 kB

Device size would be truncated, which
would corrupt data and result in
'access beyond end of device' errors.
You need to either
 * use external meta data (recommended)
 * shrink that filesystem first
 * zero out the device (destroy the filesystem)
Operation refused.

Command 'drbdmeta /dev/drbd0 v08 /dev/sda4 internal create-md' terminated with exit code 40
drbdadm aborting

Once you have confirmed that the file system present on the target partition is no longer required at the prompt type the following:

Replace /dev/sdaX with the block device you are targeting.

dd if=/dev/zero of=/dev/sdaX bs=1M count=128

Once this has completed the drbdadm create-md drbd0 command will complete with a "success."

$ drbdadm create-md drbd0
v08 Magic number not found
v07 Magic number not found
v07 Magic number not found
v08 Magic number not found
Writing meta data...
initialising activity log
NOT initialized bitmap
New drbd meta data block successfully created.
success
$

 

IF type( _session["state"] ) != "U"
    m_state = _session["state"]
    RESTORE DATASESSION FROM m_state
ELSE
    // open up your tables for the first time 
ENDIF

SAVE DATASESSION TO m_state
_SESSION["state"] = m_state

In this article Barry Mavin, CEO and Chief Software Architect for Recital provides details on how to use the Recital Universal .NET Data Provider with the Recital Database Server.

Overview

A data provider in the .NET Framework serves as a bridge between an application and a data source. A data provider is used to retrieve data from a data source and to reconcile changes to that data back to the data source.

Each .NET Framework data provider has a DataAdapter object: the .NET Framework Data Provider for OLE DB is the OleDbDataAdapter object, the .NET Framework Data Provider for SQL Server is the SqlDataAdapter object, the .NET Framework Data Provider for ODBC is the OdbcDataAdapter object, and the .NET Framework Data Provider for the Recital Database Server is the RecitalDataAdapter object.

The Recital Universal .NET Data Provider can access any data sources supported by the Recital Database Server. It is not restricted to only access Recital data. It can be used to access server-side ODBC, JDBC and OLE DB data sources also.

Core classes of the Data Provider

The Connection, Command, DataReader, and DataAdapter objects represent the core elements of the .NET Framework data provider model. The Recital Universal .NET Data Provider is plug compatible with the .NET Framework Data Provider for SQL Server. All SQL Server classes are prefixed with "Sql" e.g. SqlDataAdaptor. To use the Recital Universal Data Adaptor, simply change the "Sql" prefix to "Recital" e.g. RecitalDataAdaptor.

The following table describes these objects.

Object	Description
RecitalConnection	Establishes a connection to a specific data source.
RecitalCommand	Executes a command against a data source.
RecitalDataReader	Reads a forward-only, read-only stream of data from a data source.
RecitalDataAdapter	Populates a DataSet and resolves updates with the data source.

Along with the core classes listed in the preceding table, a .NET Framework data provider also contains the classes listed in the following table.

Object	Description
RecitalTransaction	Enables you to enlist commands in transactions at the data source.
RecitalCommandBuilder	A helper object that will automatically generate command properties of a DataAdapter or will derive parameter information from a stored procedure and populate the Parameters collection of a Command object.
RecitalParameter	Defines input, output, and return value parameters for commands and stored procedures.

The Recital Universal .NET Data Provider provides connectivity to the Recital Database Server running on any supported platform (Windows, Linux, Unix, OpenVMS) using the RecitalConnection object. The Recital Universal .NET Data Provider supports a connection string format that is similar to the SQL Server connection string format.

The basic format of a connection string consists of a series of keyword/value pairs separated by semicolons. The equal sign (=) connects each keyword and its value.

The following table lists the valid names for keyword values within the ConnectionString property of the RecitalConnection class.

Name	Default	Description
Data Source -or- Server -or- Servername -or- Nodename		The name or network address of the instance of the Recital Database Server which to connect to.
Directory		The target directory on the remote server where data to be accessed resides. This is ignored when a Database is specified.
Encrypt -or- Encryption	false	When true, DES3 encryption is used for all data sent between the client and server.
Initial Catalog -or- Database		The name of the database on the remote server.
Password -or- Pwd		The password used to authenticate access to the remote server.
User ID -or- uid -or- User -or- Username		The user name used to authenticate access to the remote server.
Connection Pooling -or- Pool	false	Enable connection pooling to the server. This provides for one connection to be shared.
Logging	false	Provides for the ability to log all server requests for debugging purposes
Rowid	true	When Rowid is true (the default) a column will be post-fixed to each SELECT query that is a unique row identifier. This is used to provide optimised UPDATE and DELETE operations. If you use the RecitalSqlGrid, RecitalSqlForm, or RecitalSqlGridForm components then this column is not visible but is used to handle updates to the underlying data source.
Logfile		The name of the logfile for logging
Gateway		Opens an SQL gateway(Connection) to a foreign SQL data source on the remote server. Using Gateways, you can transparently access the following local or remote data sources: Recital Oracle ODBC (Server-side ODBC data sources) JDBC (Server-side JDBC data sources) ADO (Use this to connect to SQL Server and other Native Windows OLEDB data sources) MySQL PostgreSQL The gateway can be specified in several formats: servertype@nodename:username/password-database e.g. oracle@nodename:username/password-database mysql@nodename:username/password-database postgresql@nodename:username/password-database -or- odbc:odbc_data_source_name_on_server oledb:oledb_connection_string_on_server jdbc:jdbc_driver_path_on_server;jdbc:Recital:args

Populating a DataSet from a DataAdaptor

The ADO.NET DataSet is a memory-resident representation of data that provides a consistent relational programming model independent of the data source. The DataSet represents a complete set of data including tables, constraints, and relationships among the tables. Because the DataSet is independent of the data source, a DataSet can include data local to the application, as well as data from multiple data sources. Interaction with existing data sources is controlled through the DataAdapter.

A DataAdapter is used to retrieve data from a data source and populate tables within a DataSet. The DataAdapter also resolves changes made to the DataSet back to the data source. The DataAdapter uses the Connection object of the .NET Framework data provider to connect to a data source and Command objects to retrieve data from and resolve changes to the data source.

The SelectCommand property of the DataAdapter is a Command object that retrieves data from the data source. The InsertCommand, UpdateCommand, and DeleteCommand properties of the DataAdapter are Command objects that manage updates to the data in the data source according to modifications made to the data in the DataSet.

The Fill method of the DataAdapter is used to populate a DataSet with the results of the SelectCommand of the DataAdapter. Fill takes as its arguments a DataSet to be populated, and a DataTable object, or the name of the DataTable to be filled with the rows returned from the SelectCommand.

The Fill method uses the DataReader object implicitly to return the column names and types used to create the tables in the DataSet, as well as the data to populate the rows of the tables in the DataSet. Tables and columns are only created if they do not already exist; otherwise Fill uses the existing DataSet schema.

Examples in C#:

////////////////////////////////////////////////////////////////////////
// include the references below
using System.Data;
using Recital.Data;

////////////////////////////////////////////////////////////////////////
// The following code example creates an instance of a DataAdapter that 
// uses a Connection to the Recital Database Server Southwind database 
// and populates a DataTable in a DataSet with the list of customers. 
// The SQL statement and Connection arguments passed to the DataAdapter 
// constructor are used to create the SelectCommand property of the DataAdapter.
public DataSet SelectCustomers()
{
	RecitalConnection swindConn = new
		RecitalConnection("Data Source=localhost;Initial Catalog=southwind");
	RecitalCommand selectCMD = new
		RecitalCommand("SELECT CustomerID, CompanyName FROM Customers", swindConn);
	selectCMD.CommandTimeout = 30;
	RecitalDataAdapter custDA = new RecitalDataAdapter();
	custDA.SelectCommand = selectCMD;
	swindConn.Open();
	DataSet custDS = new DataSet();
	custDA.Fill(custDS, "Customers");
	swindConn.Close();
	return custDS;
}

////////////////////////////////////////////////////////////////////////
// The following example uses the RecitalCommand, RecitalDataAdapter and 
// RecitalConnection, to select records from a database, and populate a 
// DataSet with the selected rows. The filled DataSet is then returned. 
// To accomplish this, the method is passed an initialized DataSet, a 
// connection string, and a query string that is a SQL SELECT statement
public DataSet SelectRecitalRows(DataSet dataset, string connection, string query) 
{
	RecitalConnection conn = new RecitalConnection(connection);
	SqlDataAdapter adapter = new RecitalDataAdapter();
	adapter.SelectCommand = new RecitalCommand(query, conn);
	adapter.Fill(dataset);
	return dataset;
}