DB String Expression

String concatenation is the most tediously manual thing in ComfyUI: you chain text nodes and concat nodes until the wires outnumber the content. DBStringExpression does it in one node with a Python expression - the string-flavored sibling of DBFloatExpression, and the node you'll reach for when your batch data needs to become a prompt.

How it works

Four string inputs - a, b, c, d - plus one expression, evaluated as Python with only those four variables in scope. The result comes back as a STRING. The README's own examples are the ones you'll use constantly:

a + b
f"{a}_{b}"

The second one is the workhorse. In a DataBeast batch, DBGetItem pulls "A puppy wearing a" and your data's color value as separate items, DBConvertToString strips them to plain strings, and f"{a}_{b}" fuses them into a full prompt. Because DBGetBatchList drives iteration, that prompt is rebuilt for every item in the batch - which is the entire reason this node is worth having.

What actually works, and what doesn't

Realistic expectations matter here. The README limits expressions to the passed-in variables, and the whole pack runs expressions through RestrictedPython. In practice that means concatenation and f-strings are the reliable operations - a + b, f"{a} {b} {c}", maybe a + b + c chains. Don't lean on fancy string methods like .upper() or .replace(); RestrictedPython is picky about attribute access, and this pack's philosophy is explicitly "limited to a, b, c, and d." When you need a transformation, do it in the data file's db_exec blocks rather than fighting the expression sandbox.

Also - the silent-failure pattern. An expression that errors returns... 0 (yes, a number, it's a copy of the float node's default), so a broken formula can hand you a numeric string downstream instead of the text you expected. Typos are quiet. Test expressions in a Python REPL first.

Installing

It ships with ComfyUI DataBeast, which is not in ComfyUI Manager yet:

cd ComfyUI/custom_nodes
git clone https://github.com/hanoixan/ComfyUI-DataBeast
cd ComfyUI-DataBeast
pip install -r requirements.txt

Restart and it's under the DataBeast category. Dependencies are just pyyaml and RestrictedPython - no models to download. Pack's still marked alpha, and V0.2 reshuffled the DBGet*/DBConvert* API, so treat any workflow you save against it as somewhat provisional.