Tables as Data Types
All
tables, which are created in MorphX by using the Application Object Tree (AOT),
can be treated like class definitions (at least in all practical aspects) in
the X++ programming language.
You
can address fields and create methods on tables. The methods can be invoked on
instances of the table.
To
manipulate (read, update, insert, and delete) records in tables, you must
declare at least one table variable, which can hold the record in focus.
Here
are a few important differences between tables and objects:
·
You cannot allocate space for table variables—it is done implicitly.
·
Fields in table variables are public—you can reference them
anywhere.
·
Fields in table variables can be referenced with expressions.
Scope of Table Variables
Table
variables are declared on the basis of the data dictionary in MorphX; that is,
on the basis of the tables, which are declared in the AOT. In most respects,
table variables can be considered objects. Contrary to objects, they are not
allocated explicitly. Only a variable declaration is required.
All
tables are compatible with the Common table in the same way that all objects are
compatible with the Object class. Table variables, which are declared
as common buffers, can be used to hold data from any table. You cannot access
tables without table variables.
Declaration of Table Variables
The
principles for declaring table variables and objects are the same except for
the allocation of space.
|
Table variable declaration
|
= ( tablename |
common ) Variable { , Variable } ;
|
public
void myMethod()
{
//
Declares and allocates space for one CustTable record
CustTable
custTable;
}
|
Note
|
|
It is a best practice to use the name of the table as
the name of the variable, but with an initial lowercase letter.
|
Referencing Table Variables
The
syntax for referencing fields in a table variable is:
RefTableVariable = Tablevariable.[ ( expression ) | fieldname ]
The
most widely used field reference is Tablevariable.Fieldname, for
example custTable.AccountNo.
public
void printAccountNo();
{
CustTable
custTable;
;
print
custTable.AccountNo;
}
The
syntax, however, also allows various possibilities for referencing fields in
records, for example by using the TableName.(FieldId) syntax. The following example prints the
contents of the fields in the current record in the Customer table.
X++
public void printCust()
{
int i, n, k;
CustTable custTable;
DictTable dictTable;
;
dictTable = new DictTable(custTable.TableId);
n = dictTable.fieldCnt();
print "Number of fields in table: ", n;
for(i=1; i<=n; i++)
{
k = dictTable.fieldCnt2Id(i);
print "The ", dictTable.fieldName(k),
" field with Id=",k, " contains '",
custTable.(k), "'";
pause;
}
}
|
Note
|
|
The previous example uses the fieldCnt and fieldCnt2Id methods. The fieldCnt method counts the number of fields in a table, while fieldCnt2Id returns the ID for a field number. For example, you can
use the fieldCnt2Id method to find out that field number 6 in a table has
the ID 54. It is necessary to perform this conversion because it is not
guaranteed that the IDs of the fields in a table are consecutive.
|
Automatic Conversion
There
is no automatic conversion, but table variables that are declared as Common can hold data from any table.
