Creating Gantt via API / SDK ?

We're looking to create a Gantt chart by inserting the data and creating the chart via the API (actually via the Java SDK, but either will do). Inserting the data is fine, but cannot seem to get the setDependenciesEnabled (which believe need for the Gantt ) or setGanttEnabled() to work…

We think part of this is the order of events, or cannot update the sheet post data insertion / updateSheet() will not take these settings (throws error)

Any ideas / suggestions would be welcome…

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Isaac A.

Hi @owlseeker!

I haven't built this specific Gantt solution with the Java SDK myself, but I did some digging into the Smartsheet API Documentation and found some constraints that seem to explain exactly why you are hitting a wall.

It looks like the issue is indeed the Order of Events, specifically regarding how projectSettings and data insertion interact.

1. The "Order of Events" Challenge You cannot enable dependencies (setDependenciesEnabled) without simultaneously telling the sheet which columns to use (mapping the startDateColumnId, durationColumnId, etc.).Since these IDs don't exist until the sheet is created, you likely need to split your process:

Create Sheet: Define your columns (Task, Start, End, Duration, Predecessors).
Get Column IDs: Parse the response to get the new IDs.
Update Project Settings: Call updateSheet to enable dependencies AND map those specific Column IDs to the project settings.

2. The "End Date" Constraint (Error 1080) The documentation notes a strict rule for dependency-enabled sheets:

"On dependency-enabled sheets, you cannot create or update End Dates directly. You must instead update the Duration or Start Date column."

If your code enables dependencies in step 3, and then tries to insert rows in step 4 by writing to the End Date column, the API will throw an error. You might need to adjust your logic to insert Start Date + Duration instead, allowing Smartsheet to calculate the End Date for you.

Since this involves specific implementation details with the Java SDK, you might also find excellent help from other developers on our Stack Overflow page.

I hope this helps you adjust the workflow!

Cheers,
Isaac.

owlseeker

But calling the sheet update with project settings throws and error of "to update projectSettings you must first enable dependencies" - there is no API specific call to enable dependencies, and if I try setting this through the sheet update (separate or combined call) you get the error ""sheet.dependencies are not allowed for this operation" - there is no other operation that I can see to set dependencies (cannot set when sheet is created either - throws the same error)

Isaac A.

Hi @owlseeker!

Thank you for sharing those specific error messages, that changes everything.

As I mentioned before, I haven't built this specific solution myself, so I was basing my previous suggestions on the general update logic. However, after seeing your errors, I did a much deeper review of our documentation regarding Columns and Project Settings, and I need to correct my earlier advice.

It turns out this isn't just an "order of operations" issue—it looks like a hard limitation of the API regarding how Project Sheets are configured.

1. Column Type Restrictions: To enable dependencies, a sheet requires specific column types (like DURATION for duration and ABSTRACT_DATETIME for predecessors). However, according to the Columns API Reference:

"The API does not support setting a column to this type. (This can only be done through the Smartsheet Web app when configuring a project sheet.)"

Furthermore, while dependencies are enabled, you cannot change the type of any special calendar/Gantt columns. To change these types, dependencies must first be disabled.

2. Project Settings Limitations: Additionally, when looking at the Update Sheet endpoint, the projectSettings object is quite limited. The documentation only lists attributes like lengthOfDay, nonWorkingDays, and workingDays.Although the sheet response contains a dependenciesEnabled boolean, the request documentation does not include a specific field to easily toggle this setting on or off without the proper column structure already in place.

My Recommendation given these restrictions, it sounds like creating the sheet entirely from scratch via the API might not be possible for this specific use case.

Instead, you might want to try creating the sheet in the Smartsheet Web App first (where you can manually enable dependencies and set the column types), and then use the API to Copy that sheet or use it as a template. That way, the structure is already there before you try to insert the data.

Since this involves specific implementation details, I highly recommend checking out our Stack Overflow page. There are many active developers there who can likely confirm if this is the best path forward.

I hope this saves you from further debugging!

Cheers,
Isaac.

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