feat: add optional DuckDB query source

DESCRIPTION

@@ -27,7 +27,8 @@ Imports:
     sf,
     methods
 Suggests:
-    testthat
+    testthat,
+    duckdb
 License: GPL (>= 3)
 Encoding: UTF-8
 LazyData: true
@@ -44,6 +45,7 @@ Collate:
     'query.R'
     'query_source.R'
     'query_source_arrow.R'
+    'query_source_duckdb.R'
     'query_source_sf.R'
     'query_subset.R'
     'sf_arrow.R'

NAMESPACE

@@ -17,6 +17,7 @@ export(query_set_layers)
 export(query_set_sink)
 export(query_set_source)
 export(query_source_arrow)
+export(query_source_duckdb)
 export(query_source_sf)
 export(query_subset)
 export(read_sf_dataset)

R/query_source_duckdb.R

@@ -0,0 +1,47 @@
+#' Create a new DuckDB query source
+#' @param srcname Path or URI to source
+#' @param ... Passed to [DBI::dbConnect].
+#' @param .attach If `TRUE`, then `ATTACH <srcname>` is executed on the DuckDB connection
+#' @param .extensions Optional extensions to install and load on connection
+#' @returns An `hfsubset_query_source_duckdb` object
+#' @export
+query_source_duckdb <- function(srcname, ..., .attach = FALSE, .extensions = c("spatial")) {
+  if (!requireNamespace("duckdb", quietly = TRUE)) {
+    stop("Package `duckdb` is required for query_source_duckdb()")
+  }
+
+  conn <- DBI::dbConnect(duckdb::duckdb(), ...)
+
+  for (ext in .extensions) {
+    DBI::dbExecute(conn, paste("INSTALL", ext))
+    DBI::dbExecute(conn, paste("LOAD", ext))
+  }
+
+  if (.attach) {
+    DBI::dbExecute(
+      conn,
+      paste0("ATTACH '", srcname, "' AS hydrofabric (TYPE SQLITE)")
+    )
+  }
+
+  structure(
+    list(src = srcname, conn = conn),
+    class = c("hfsubset_query_source_duckdb", "hfsubset_query_source")
+  )
+}
+
+#' @method query_source_layer hfsubset_query_source_duckdb
+#' @keywords internal
+query_source_layer.hfsubset_query_source_duckdb <- function(query_source, layer, ..., query = NULL) {
+  if (missing(layer) && !is.null(query)) {
+    dplyr::tbl(query_source$conn, dbplyr::sql(query), ...)    
+  } else {
+    dplyr::tbl(query_source$conn, paste0("hydrofabric.", layer), ...)
+  }
+}
+
+#' @method query_source_layers hfsubset_query_source_duckdb
+#' @keywords internal
+query_source_layers.hfsubset_query_source_duckdb <- function(query_source, ...) {
+  DBI::dbListTables(query_source$conn)
+}

R/zzz.R

@@ -16,7 +16,8 @@
 
   query_source_classes <- c(
     "hfsubset_query_source_arrow",
-    "hfsubset_query_source_sf"
+    "hfsubset_query_source_sf",
+    "hfsubset_query_source_duckdb"
   )
 
   for (query_source_class in query_source_classes) {