add a detailed example of the usage of multi-select fields with many …

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examples/todo application (PostgreSQL)/batch.sql

@@ -0,0 +1,98 @@
+-- Include 'shell.sql' to generate the page header and footer
+select 'dynamic' as component, sqlpage.run_sql('shell.sql') as properties;
+
+-- Define a Common Table Expression (CTE) named 'updated'
+-- CTEs are temporary named result sets, useful for complex queries
+-- Here, it's used to perform the update and capture the results in one step
+with updated as (
+    -- Update the 'todos' table and return the modified rows
+    -- This approach allows us to both update the data and use it for reporting
+    update todos set
+    -- Modify the title based on user input for labels
+    -- The CASE statements handle different scenarios for label management
+    title = case 
+        -- If :remove_label is null, we keep the existing title as is
+        when :remove_label is null then
+            title
+        else  
+            -- Remove any existing labels (text within parentheses)
+            -- This uses a regular expression to strip out (label) from the end
+            regexp_replace(title, '\s*\(.*\)', '')
+        end
+        -- Concatenate the result with a new label if provided
+        ||
+        case 
+            -- If no new label is provided, we don't add anything
+            when :new_label is null or :new_label = '' then
+                ''
+            else
+                -- Add the new label in parentheses at the end
+                ' (' || :new_label || ')'
+        end
+    -- Determine which todos to update based on user selection
+    where 
+        -- Update specific todos if their IDs are in the :todos parameter
+        -- :todos is a JSON array of todo string IDs, e.g. ["1", "2", "3"]
+        -- that optionally includes "all" to update all todos
+        id in (
+            -- Parse the JSON array of todo IDs and convert each to integer
+            -- This allows for multiple todo selection in the UI
+            select e::int from jsonb_array_elements_text(:todos::jsonb) e 
+            where e != 'all'
+        )
+        -- If 'all' is the only selected, update every todo (by making the where condition always true)
+        or :todos = '["all"]'
+    -- Return all updated rows for counting and potential further use
+    returning *
+)
+-- Generate an alert component to inform the user about the update result
+-- This provides immediate feedback on the operation's outcome
+select 'alert' as component,
+    'Batch update' as title,    
+    -- Create a dynamic message with the count of updated todos
+    format('%s todos updated', (select count(*) from updated)) as description
+-- Only display the alert if at least one todo was updated
+-- This prevents showing unnecessary alerts for no-op updates
+where exists (select * from updated);
+
+-- Create a form component for the batch update interface
+-- This sets up the structure for the user input form
+select 'form' as component,
+    'Batch update' as title,
+    'Update all todos' as contents;
+
+-- Create a select input for choosing which todos to update
+-- This allows users to pick multiple todos or all todos for updating
+select 
+    'select' as type,
+    'Update these todos' as label,
+    'todos[]' as name,
+    true as multiple,
+    true as dropdown,
+    true as required,
+    -- Combine a static "all" option with dynamic options for each todo
+    -- This uses JSON functions to build a complex data structure for the UI
+    -- The JSON structure is used to set the label, value, and selection state for each option
+    -- The generated JSON looks like this:
+    -- [{"label":"Update all todos","value":"all","selected":true},{"label":"Todo 1","value":"1","selected":false}]
+    jsonb_build_array(jsonb_build_object( -- json_build_object takes a list of key-value pairs and returns a JSON object
+        'label', 'Update all todos', -- The label of the option
+        'value', 'all', -- The value of the option
+        'selected', :todos = '["all"]' or :todos is null -- Pre-select 'all' only if it was previously chosen or if :todos is not set (the page was just loaded)
+    )) ||
+    -- Generate an option for each todo in the database
+    jsonb_agg(jsonb_build_object(
+        'label', title,
+        'value', id,
+        -- Pre-select this todo if it was in the previous selection
+        'selected', (id in (select e::int from jsonb_array_elements_text(:todos::jsonb) e where e != 'all'))
+    )) as options
+from todos;
+
+-- Create a text input for entering a new label
+-- This allows users to specify the label to be added to the selected todos
+select 'new_label' as name, 'New label' as label;
+
+-- Create a checkbox for optionally removing existing labels
+-- This gives users the choice to strip old labels before adding a new one
+select 'checkbox' as type, 'Remove previous labels' as label, 'remove_label' as name;

examples/todo application (PostgreSQL)/shell.sql

@@ -1,6 +1,7 @@
 select
     'shell' as component,
     format ('Todo list (%s)', count(*)) as title,
+    'batch' as menu_item,
     'timeline' as menu_item
 from
     todos;