table.RELATION_ADD Function

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Syntax

V Relation_Add(P Table), Specify the required values in the Relation dot variable, then use the following command: <TBL>.RELATION_ADD( <Child_Table> as P )

Arguments

Table

A pointer to the table that will become a child to parent <TBL>.

Description

Add a relation to a table.

Relation.link_type

Type "N". Describes the relationship between the parent and child tables. The Link Type parameter can be assigned one of four types of links:

Link Type

Type Description

LINK_MANY

One record from the parent table is related to one or more records in the child table.

LINK_FIRST

One record from the parent table is related to the first matching record in the child table.

LINK_LAST

One record from the parent table is related to the last matching record in the child table.

LINK_CLOSEST

One record from the parent table is related to the closest matching record in the child table.

Relation.index_child

Type "P". To link tables, the linking field(s) in the child table must be indexed. To specify the linking index, assign the Relation.index_child a pointer to an existing index.

Relation.order_parent

Type "C". Indicates which field or combination of fields in the parent table are used to link to the indexed field(s) in the child table. In most cases, the expression used in the linking index and the common linking expression are similar (i.e., the parent and child table are linked on a single field, with identical field names).

Relation.ref_integrity

Type "N". A numeric value that indicates how referential integrity is to be enforced on the link. The referential integrity parameter can be set to: 0 = no integrity 1 = cascade changes 2 = prevent changes For more information on referential integrity, see "Using the Set Editor" in the User's Guide.

 Discussion

The <TBL>.RELATION_ADD() method establishes a relationship, or link, between two open tables. The link definition determines the nature of this relationship. It is established through the relation function variable, as shown in the syntax diagram above. The <TBL>.RELATION_ADD() method uses the contents of the relation function variable when constructing the link. The parent table of the link is the table referenced by the object pointer, <TBL>, and the child table of the link is the table referenced by the object pointer, <Child_Table> pointer. You can use <TBL>.RELATION_ADD()with two or more open tables to form a set design. You can then save this set as a set definition file using the <TBL>.SET_CREATE() method. When the collection of tables linked by <TBL>.RELATION_ADD()is complete, you can store it in a set definition using the <TBL>.SET_CREATE() method. A set is referenced by the table pointer of the set's primary table.

 Example

This script uses the relation add method to find the number of invoices for an individual customer.

dim parent as P
dim parent_index as P
id = ui_get_text("Count Invoices","For which customer ID? ","C001")
if id = "" then
    end
end if
parent = table.open("c:\a5\a_sports\customer.dbf")
parent_index = parent.index_primary_put("CUST_ID")
result = parent.fetch_find(id)
if (result < 0) then
    ui_msg_box("Error", "Customer not found.")
    end
end if
child_tbl = table.open("c:\a5\a_sports\inv_head.dbf")
relation.link_type = LINK_MANY
child_index = child_tbl.index_get("CUST_ID")
relation.index_child = child_index
relation.order_parent = "CUST_ID"
relation.ref_integrity = 0
parent.relation_add(child)
' or parent.relation.change()if the relationship exists but is being changed
count = 0
child_tbl.fetch_first()
while .NOT. child_tbl.fetch_eof()
    count = count + 1
    child_tbl.fetch_next()
end while
trace.writeln("Number of invoices for customer: " + ltrimcount?)
parent.relation_drop(child)
child_tbl.close()

See Also