Expression Builder

The Expression Builder is a development environment for working with the Expression Language. This component can be opened when editing Expression fields in the Properties Editor and contains tools for efficiently testing and building expressions throughout Iotellect.

The default view of the Expression Builder is pictured below.

  • The Help Text Area at the top displays summary information about the specific expression field being edited, if such information is available. The example below is from a Web dashboard binding expression.

  • The Entity Selector in the left pane allows referring Iotellect Server contexts, variables, functions, events, and even specific fields and rows from their data table formats. Hovering over an item in the tree reveals buttons to copy or directly insert the absolute reference to the entity.

  • The Components area is a tab in the left pane and contains an Entity Selector for finding references to dashboard component properties. This section is available only when editing dashboard binding expressions.

  • Expression Text Area is the middle pane and acts as a text editor, as well as displaying the default context where the expression will be evaluated and giving the option to change to a different context.

    • Clicking the menu button under the Default Context label gives the option to choose a different default context.

    • Evaluation Mode indicates whether the expression should be evaluated on the server () or in the browser (). Evaluation in the browser can be faster, but evaluation results may differ since server-side and browser-side expression features and functions are slightly different.

    • The Evaluate button processes the entire expression in the selected context. Evaluate a portion of the expression by selecting the desired text and pressing Ctrl+Enter or clicking Evaluate.

    • The Save button will save the current text to the expression field being edited.

  • Function Chooser in the right pane allows searching, selecting, and inserting functions, as well as indicating the parameters and their type.

  • Reference Editor is tabbed in the right pane, and allows the currently selected reference in the expression area to be edited. Any part of a reference may be changed independently. When changes are made, the expression text is updated. The Resolve button allows available values to be retrieved.

  • The Events pane in the bottom center displays a list of events that have been triggered while evaluating expressions.

Evaluating Expressions in the Builder

The Expression Builder allows you to validate the syntax of any expression. In cases where data is available in the default context, it's also possible to calculate the result that the expression will produce. This can be done since Expression Builder knows about the evaluation environment of the current expression. However, the evaluation environment is not always complete, and in some cases, it's not possible to evaluate the expression correctly from the Expression Builder. Here are some examples:

  • If editing an event filter expression, there is no specific event that provides data for the expression.

  • Similarly, an alert event trigger expression cannot be evaluated within the expression builder because there is no alert data until the alert is triggered.

The Expression Builder includes a toggle to select whether the expressions evaluated in the editor will be evaluated on the server () or in the browser (). Note that this toggle only affects expression evaluation in the Expression Builder. Expressions in production (for example, in a binding, or validity expression) are mostly evaluated on the server, and only in a few cases production evaluation takes place in a browser.

  • Browser Evaluation can be faster, but not all functions are evaluated in the same way as on the server. Therefore, browser evaluation is principally to check that a given expresion has the correct syntax to be evaluated.

  • Server Evaluation is the default evaluation mode, and ensures greater accuracy by evaluating all expression functions in the same way as they will be evaluated in production. While server evaluation can be slower, it must be used when evaluating the results of expression evaluation. Obviously, this mode should not be used to debug expressions that will be later evaluated in a browser.

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