Allow db_query_fields to work with queries and tables

Fixes #218

NEWS.md

@@ -43,6 +43,8 @@ The old API has been soft-deprecated - it will continue to work, but no further
 
 ## Other bug fixes and improvements
 
+* The dplyr interface can work with literal SQL once more (#218).
+
 * The DBI interface has been updated to use the new low-level API.
   This means that it defaults to using modern SQL not legacy SQL.
   Use `use_legacy_sql = TRUE` in `DBI::dbConnect()` if you need to use

R/bq-query.R

@@ -82,7 +82,7 @@ bq_dataset_query <- function(x, query,
 
 # Similar to bq_perform_query: except uses dryRun, and hence result
 # processing is totally different
-bq_query_fields <- function(query, x, ..., use_legacy_sql = FALSE) {
+bq_query_fields <- function(query, x, ..., default_dataset = NULL, use_legacy_sql = FALSE) {
   assert_that(is.string(x), is.string(query))
 
   url <- bq_path(x, jobs = "")
@@ -91,6 +91,10 @@ bq_query_fields <- function(query, x, ..., use_legacy_sql = FALSE) {
     query = unbox(query),
     useLegacySql = unbox(use_legacy_sql)
   )
+  if (!is.null(default_dataset)) {
+    query$defaultDataset <- datasetReference(default_dataset)
+  }
+
   body <- list(configuration = list(query = query, dryRun = TRUE))
 
   res <- bq_post(

R/dplyr.R

@@ -60,8 +60,15 @@ tbl.src_bigquery <- function(src, from, ...) {
 
 # registered onLoad
 db_query_fields.BigQueryConnection <- function(con, sql) {
-  info <- get_table(con@project, con@dataset, sql)
-  vapply(info$schema$fields, "[[", "name", FUN.VALUE = character(1))
+  if (dbplyr::is.sql(sql)) {
+    ds <- bq_dataset(con@project, con@dataset)
+    fields <- bq_query_fields(sql, con@billing, default_dataset = ds)
+  } else {
+    tb <- bq_table(con@project, con@dataset, sql)
+    fields <- bq_table_fields(tb)
+  }
+
+  vapply(fields, "[[", "name", FUN.VALUE = character(1))
 }
 
 # SQL translation -------------------------------------------------------------

tests/testthat/test-dplyr.R

@@ -1,5 +1,17 @@
 context("dplyr.R")
 
+test_that("can work with literal SQL", {
+  con_us <- DBI::dbConnect(
+    dbi_driver(),
+    project = "bigquery-public-data",
+    dataset = "utility_us",
+    billing = bq_test_project()
+  )
+
+  x <- tbl(con_us, sql("SELECT * FROM country_code_iso"))
+  expect_true("fips_code" %in% dbplyr::op_vars(x))
+})
+
 test_that("casting uses bigquery types", {
   skip_if_not_installed("dbplyr")