I have a PostGIS multipolygon layer in the map view and want to bring the feature selection into the print composer. Also, only the label for the selected feature should be visible in the map I want to create.
Define a coverage layer - this in your case is the polygon layer. If you set up an atlas in the print composer, QGIS will produce a separate sheet zoomed to each feature of the polygon layer - thus it will do automatically what you did by hand using a selection. All the additional information on the sheet can be configured in the item properties.
To set up an atlas, click the
menu Atlas in the print composer and select
atlas settings. There, you can click
generate an atlas, than define your coverage layer. Than click the map in your print composer and in item settings
Controlled by Atlas.
For all elements present in your print composer, you can than set conditions that depend on the current atlas feature - you have at your hand several variable in the expression editor like
@atlas_featureid etc. that allows you to configure detailed conditions on what should be visible on each individual sheet.