Workflow automation for populating QGIS Attribute table

Question

Is there a tool in QGIS which populates fields within the attribute table?

I know I can edit it manually but what I want is to include that tool in the workflow automation process.

I want to label the output rather than put it on the key of the map. To label I need to have a field where I can add the label. Since this is part of a larger process in the Graphical Modeler I need to automate it rather than adding the field and name manually.

What I'm interested in is if there is a tool or Expression in the Field Calculator that can return the name of the input layer and add it to the attribute table of the new/ output layer of the Field Calculator tool

Answer 1

There are several options I may refer you to:

1. "Field calculator" : qgis:fieldcalculator

   Opens the field calculator. You can use all the supported expressions and functions.

   A new layer is created with the result of the expression.

   The field calculator is very useful when used in The graphical modeler.

2. "Refactor fields" : qgis:refactorfields

   Allows editing the structure of the attribute table of a vector layer.

   Fields can be modified in their type and name, using a fields mapping.

   The original layer is not modified. A new layer is generated, which contains a modified attribute table, according to the provided fields mapping.

   Refactor layer fields allows to:

   • Change field names and types
   • Add and remove fields
   • Reorder fields
   • Calculate new fields based on expressions
   • Load field list from another layer

3. Advanced Python field calculator : qgis:advancedpythonfieldcalculator

   Adds a new attribute to a vector layer, with values resulting from applying an expression to each feature.

   The expression is defined as a Python function.

4. Execute SQL : qgis:executesql

   Runs a simple or complex query with SQL syntax on the source layer.

   Beside a simple query, you can add expressions or variables within the SQL query parameter itself. This is particulary useful if this algorithm is executed within a Processing model and you want to use a model input as a parameter of the query. An example of a query will then be SELECT * FROM [% @table %] where @table is the variable that identifies the model input.

   The result of the query will be added as a new layer.

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Answering the question "Expression in the Field Calculator that returns the name of the input layer?"

As was mentioned by @AlexandreNeto:

you can get the layer name using the variable /@layer_name, there is also the /@layer_id.

Check these article for more details:

• EXPLORING VARIABLES IN QGIS 2.12, PART 1
• EXPLORING VARIABLES IN QGIS PT 2: PROJECT MANAGEMENT
• EXPLORING VARIABLES IN QGIS PT 3: LAYER LEVEL VARIABLES