How-to guide · how to add a lookup table to a dynamic block

How to add a lookup table to a dynamic block in AutoCAD

DWGDXFFree1,072 words

By Saumyajit Maity · Published 27 Apr 2022 · Updated 28 Jun 2024

A lookup table turns a dynamic block's raw parameters into a friendly dropdown of named choices. Instead of dragging a stretch grip to exactly 900 and a second grip to exactly 600, the user picks Standard or Large from a list and every parameter sets itself to the right value at once. It is how you give a block a real catalogue of sizes — the most professional touch a dynamic block can have.

The lookup table maps input parameter values to a readable label, and optionally works in reverse: change the parameters and the dropdown shows which named size matches. Behind it sits a Lookup parameter and a Lookup action, plus the constrained parameters whose values the table drives. It rewards a little planning, because the table only makes sense once your stretches and flips already snap to discrete values.

This guide builds a lookup table on top of existing dynamic behaviour, so it assumes your block already has at least one constrained parameter — for example a stretch limited to a list of lengths — and shows how to wrap those in a single named dropdown.

Step 1 — Constrain your parameters first

A lookup table can only map to discrete values, so before you add one, make sure the parameters it will drive are constrained. Open the block with BEDIT and set each relevant Linear or other parameter's Distance Type (or Angle Type) to List or Increment, so it has a finite set of allowed values rather than a free range.

This step is the foundation. If a stretch is still free-ranging, the lookup table has no clean values to snap it to, and the dropdown will not behave predictably. Get every parameter that the table will control onto a tidy set of allowed values first.

Step 2 — Add the Lookup parameter and action

On the Parameters tab, click Lookup and place its grip where the dropdown arrow should appear, usually just outside the block. Then on the Actions tab, click Lookup, select the Lookup parameter, and AutoCAD opens the Property Lookup Table dialog. This dialog is where the whole table is built.

Unlike other actions, the Lookup action does not ask you to select geometry — it works on parameter values, not lines. Its job is to read and write the values of the other parameters, so the only thing it needs is the table you are about to fill in.

Step 3 — Build the lookup table

In the Property Lookup Table dialog, click Add Properties and choose the input parameters you want the table to control — say Length and Depth. Each becomes an input column. Then add rows: for each row, type the value each input parameter should take, and in the Lookup column type the friendly name for that combination, such as Small, Standard or Large.

Work down the table one named size per row, entering the exact allowed values for each parameter. Because the inputs are constrained to a list, you should be typing values that already exist in each parameter's allowed set; a value that does not match the parameter's list will not resolve cleanly.

Step 4 — Make the lookup work in reverse

By default a lookup is one-way: pick a name and the parameters set themselves. You can make it two-way so that if a user manually drags the stretch grips to a combination that matches a row, the dropdown updates to show that name. In the Lookup column header, set the property to Allow Reverse Lookup.

Reverse lookup is worth turning on because it keeps the named size and the actual geometry in agreement. Without it, someone could stretch the block to Large dimensions while the dropdown still says Standard, which is confusing on a schedule. With it on, the label always reflects reality when the geometry matches a defined size.

Pitfalls with lookup tables

The number-one mistake is building the table before constraining the parameters, so the lookup has nothing clean to snap to. Always constrain to List or Increment first. The second is typing a value into the table that is not in a parameter's allowed list — it will not resolve, and that named size will appear broken.

A third issue is forgetting reverse lookup, which leaves the label and the geometry able to drift apart. Turn it on unless you have a reason not to. Finally, keep the lookup names human and consistent — Small, Medium, Large, or real catalogue codes — because those names are what a colleague sees in the dropdown and what may flow into a schedule, so they should read like product sizes, not internal jargon.

Free download

Browse the full library — DWG & DXF, no signup.

Download CAD blocks

Questions

Frequently asked

Do I need other parameters before adding a lookup table?+

Yes. A lookup table drives existing parameters, so the block needs at least one constrained parameter — a stretch limited to a list of values, for example — before the table has anything meaningful to set.

Why does a named size only set some of the dimensions?+

That table row is missing a value, or a value you typed is not in the parameter's allowed list. Open the Property Lookup Table, check every cell in the row, and use only values the parameters permit.

What is reverse lookup and should I enable it?+

Reverse lookup updates the dropdown name when a user manually drags the grips to a combination that matches a defined size. Enable it so the named size and the actual geometry always agree.

Can one lookup table control several parameters at once?+

Yes — that is the point. Add each parameter as an input column, then each row sets all of them together. Picking one name can resize length, depth and more in a single click.

Related downloads