An Expression is ultimately just a human-readable string and can be written by hand.
However at run-time Expressions are created using AdapTable's Expression Editor.
This visual has a number of useful features including:
Drag n Drop of Columns into the Editor
Lists all available functions in a dropdown so they can be immediately applied in the Editor
This list will include any custom functions provided at design-time
Provides common operators as buttons above the Editor
Ensures that the functions and operators are suitable for the type of Expression being created (e.g. Observable, Scalar etc)
Displays a row of data from the Grid organised by Column for scenario analysis
By default the data is taken from the first row of the Grid, but it can be edited by the user in order to try out different scenarios
Highlights the return value of the Expression
Context sensitive Support / Help for each available function - the Editor explains what the function does, shows its definition and provides an example
Links to this Help Site for more detailed information on writing Expressions and the different Query options
showDocumentationLinksto false in User Interface Options to turn this off
Displays a warning - and prevents the user from continuing - if the Expression is not valid