How to change geometry type from LINESTRING to MULTILINESTRING in a Postgresql database layer in QGIS

Question

I merged lines in a shapefile layer and need to copy them to a postgreSQL database layer. If I paste them to the pg db layer, it does not work. If I merge them, after I pasted to QGIS, it crashes. I figured out that it works, if I export the pg db layer to a geopackage or shapefile layer and set the geometry from linestring to multilinestring. The problem is that I need it to bring to the data base layer. Anyone can give me a hint how I configure the db layer in the right way?

Thank you!

Answer 1

I would change the geometry type in PostgreSQL not in the geopackage or shapefile. The problem seems to be in the geometry type column. You could use this to change it:

ALTER TABLE [table_name]
        ALTER COLUMN [geometry_column] TYPE geometry(MULTILINESTRING) USING ST_Multi([geometry_column]);

OR

You could import in PostgreSQL the lines without merging them and to that in with postgis while altering the geometry type of the column:

ALTER TABLE [table_name]
        ALTER COLUMN [geometry_column] TYPE geometry(MULTILINESTRING) USING ST_Union([geometry_column]);

Also, this might help you: https://gis.stackexchange.com/questions/68071/how-to-create-a-multilinestring-feature-with-a-postgis-layer-in-qgis