A dereference expression gets the value of a column from a specific row of another table. A dereference expression makes use of references between tables, using the value of a column of type
Ref in this table to find a specific row in another table and get a value from a column there.
To learn how to create a dereference, check out this video:
The following sections describe dereference expressions in more detail:
New to expressions and formulas? See Expressions: The Essentials.
A dereference expression is of the form:
ref-column is the name of the column of type
Ref in the this table, and
value-column is the name of a column of the other table.
The configuration of a column of type
Ref identifies the table in which referenced rows are to be found:
The value of a
Ref column should be the key column value of a row in the
Ref column's source table.
The Order Deliveries sample app includes a typical dereference expression. The
Orders table uses the dereference expression,
[Customer ID].[Email], to retrieve the customer email from the
Customers table based on the customer ID. This dereference expression can be thought to mean:
Go to the source table identified
In that source table, find the row with a key column value that matches the
Customer IDcolumn of this row.
From that row in the source table, get the value of the
A column value of type
EnumList with a base type of
Ref can be dereferenced to produce a new list of the values from dereferencing each individual reference, an operation called a list dereference.
A list dereference is performed by enclosing the
Ref list column name (such as,
Related Orders) and the column name of the desired column value (such as,
Order Date) each in square brackets (
]) and placing them adjacent to each other:
[Related Orders][Order Date]
The result will be a list of
Order Date column values from the rows identified by the list in the
Related Orders column value.
See also Build list dereferences.
You can dereference a dereference.
For example, you might have a three-level hierarchy consisting of a
Customer row, a child
Order row, and a grandchild
Order Detail row. The
Order Detail row contains a reference to the
Order row. The
Order row contains a reference to the
Order Detail row, you can directly access the value of a column in the
Customer row by chaining dereference expressions. That is, you can dereference from the
Order Detail row to the
Order row, and then dereference from the
Order row to the
Customer row in a single expression.
[Order Id].[Customer Name].[Email]