chore: Rework list_tables()

Original: 7730f13

refactor `dbListTables()` with `list_tables()`, now orders result by `table_type` and `table_name`
refactor `dbExistsTable()` with `list_tables()`
refactor `dbListObjects()` with `list_tables()`
merge `find_table()` code into `list_fields()`
`find_table()` isn't used anywhere else anymore (e.g. `exists_table()`)
simplify the "get current_schemas() as table" code
pass full `id` to `list_fields()`
align `dbExistsTable()` with `dbListFields()`
simplify `where_schema` in `list_tables()`
align `where_table` with `where_schema` in `list_tables()`

Author: dpprdan

R/dbExistsTable_PqConnection_character.R

@@ -2,10 +2,11 @@
 #' @usage NULL
 dbExistsTable_PqConnection_character <- function(conn, name, ...) {
   stopifnot(length(name) == 1L)
-  name <- dbQuoteIdentifier(conn, name)
-
-  # Convert to identifier
-  id <- dbUnquoteIdentifier(conn, name)[[1]]
+  # use (Un)QuoteIdentifier roundtrip instead of Id(table = name)
+  # so that quoted names (possibly incl. schema) can be passed to `name` e.g.
+  # name = dbQuoteIdentifier(conn, Id(schema = "sname", table = "tname"))
+  quoted <- dbQuoteIdentifier(conn, name)
+  id <- dbUnquoteIdentifier(conn, quoted)[[1]]
   exists_table(conn, id)
 }
 

R/dbListFields_PqConnection_Id.R

@@ -1,7 +1,7 @@
 #' @rdname postgres-tables
 #' @usage NULL
 dbListFields_PqConnection_Id <- function(conn, name, ...) {
-  list_fields(conn, name)
+  list_fields(conn, id = name)
 }
 
 #' @rdname postgres-tables

R/dbListObjects_PqConnection_ANY.R

@@ -13,10 +13,13 @@ dbListObjects_PqConnection_ANY <- function(conn, prefix = NULL, ...) {
       null_varchar <- "NULL::text"
     }
     query <- paste0(
-      "SELECT ", null_varchar, " AS schema, table_name AS table FROM INFORMATION_SCHEMA.tables\n",
-      "WHERE (table_schema = ANY(current_schemas(true))) AND (table_schema <> 'pg_catalog')\n",
+      "SELECT ", null_varchar, " AS schema, table_name AS table FROM ( \n",
+        list_tables(conn = conn, order_by = "table_type, table_name"),
+      ") as table_query \n",
       "UNION ALL\n",
-      "SELECT DISTINCT table_schema AS schema, ", null_varchar, " AS table FROM INFORMATION_SCHEMA.tables"
+      "SELECT DISTINCT table_schema AS schema, ", null_varchar, " AS table FROM ( \n",
+        list_tables(conn = conn, where_schema = "true"),
+      ") as schema_query;"
     )
   } else {
     if (!is.list(prefix)) prefix <- list(prefix)
@@ -27,10 +30,20 @@ dbListObjects_PqConnection_ANY <- function(conn, prefix = NULL, ...) {
     schemas <- vcapply(prefix[is_prefix], function(x) x@name[["schema"]])
     if (length(schemas) > 0) {
       schema_strings <- dbQuoteString(conn, schemas)
+      where_schema <-
+        paste0(
+          "table_schema IN (",
+          paste(schema_strings, collapse = ", "),
+          ") \n"
+        )
       query <- paste0(
-        "SELECT table_schema AS schema, table_name AS table FROM INFORMATION_SCHEMA.tables\n",
-        "WHERE ",
-        "(table_schema IN (", paste(schema_strings, collapse = ", "), "))"
+        "SELECT table_schema AS schema, table_name AS table FROM ( \n",
+          list_tables(
+            conn = conn,
+            where_schema = where_schema,
+            order_by = "table_type, table_name"
+          ),
+        ") as table_query"
       )
     }
   }

R/dbListTables_PqConnection.R

@@ -1,12 +1,9 @@
 #' @rdname postgres-tables
 #' @usage NULL
 dbListTables_PqConnection <- function(conn, ...) {
-  query <- paste0(
-    "SELECT table_name FROM INFORMATION_SCHEMA.tables ",
-    "WHERE ",
-    "(table_schema = ANY(current_schemas(true))) AND (table_schema <> 'pg_catalog')"
-  )
-  dbGetQuery(conn, query)[[1]]
+  query <- list_tables(conn = conn, order_by = "table_type, table_name")
+
+  dbGetQuery(conn, query)[["table_name"]]
 }
 
 #' @rdname postgres-tables

R/tables.R

@@ -120,26 +120,72 @@ db_append_table <- function(conn, name, value, copy, warn) {
   nrow(value)
 }
 
+list_tables <- function(conn, where_schema = NULL, where_table = NULL, order_by = NULL) {
+
+  query <- paste0(
+    # information_schema.table docs: https://www.postgresql.org/docs/current/infoschema-tables.html
+    "SELECT table_schema, table_name \n",
+    "FROM information_schema.tables \n",
+    "WHERE TRUE \n" # dummy clause to be able to add additional ones with `AND`
+  )
+
+  if (is.null(where_schema)) {
+    # `true` in `current_schemas(true)` is necessary to get temporary tables
+    query <- paste0(
+      query,
+      "  AND (table_schema = ANY(current_schemas(true))) \n",
+      "  AND (table_schema <> 'pg_catalog') \n"
+    )
+  } else {
+    query <- paste0(query, "  AND ", where_schema)
+  }
+
+  if (!is.null(where_table)) query <- paste0(query, "  AND ", where_table)
+
+  if (!is.null(order_by)) query <- paste0(query, "ORDER BY ", order_by)
+
+  query
+}
+
 exists_table <- function(conn, id) {
   name <- id@name
+  stopifnot("table" %in% names(name))
+  table_name <- dbQuoteString(conn, name[["table"]])
+  where_table <- paste0("table_name = ", table_name, " \n")
 
+  if ("schema" %in% names(name)) {
+    schema_name <- dbQuoteString(conn, name[["schema"]])
+    where_schema <- paste0("table_schema = ", schema_name, " \n")
+  } else {
+    where_schema <- NULL
+  }
   query <- paste0(
-    "SELECT COUNT(*) FROM ",
-    find_table(conn, name)
+    "SELECT EXISTS ( \n",
+    list_tables(conn, where_schema = where_schema, where_table = where_table),
+    ")"
   )
-
-  dbGetQuery(conn, query)[[1]] >= 1
+  dbGetQuery(conn, query)[[1]]
 }
 
-find_table <- function(conn, id, inf_table = "tables", only_first = FALSE) {
+list_fields <- function(conn, id) {
+  name <- id@name
+
   is_redshift <- is(conn, "RedshiftConnection")
 
-  if ("schema" %in% names(id)) {
+  # get relevant schema
+  if ("schema" %in% names(name)) {
+    # either the user provides the schema
     query <- paste0(
       "(SELECT 1 AS nr, ",
-      dbQuoteString(conn, id[["schema"]]), "::varchar",
+      dbQuoteString(conn, name[["schema"]]), "::varchar",
       " AS table_schema) t"
     )
+
+    # only_first not necessary,
+    # as there cannot be multiple tables with the same name in a single schema
+    only_first <- FALSE
+
+  # or we have to look the table up in the schemas on the search path
   } else if (is_redshift) {
     # A variant of the Postgres version that uses CTEs and generate_series()
     # instead of generate_subscripts(), the latter is not supported on Redshift
@@ -158,25 +204,31 @@ find_table <- function(conn, id, inf_table = "tables", only_first = FALSE) {
     )
     only_first <- FALSE
   } else {
-    # https://stackoverflow.com/a/8767450/946850
+    # Get `current_schemas()` in search_path order
+    # so $user and temp tables take precedence over the public schema (by default)
+    # https://www.postgresql.org/docs/current/ddl-schemas.html#DDL-SCHEMAS-PATH
+    # https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-SEARCH-PATH
+    # How to unnest `current_schemas(true)` array with element number (works since v9.4):
+    # https://stackoverflow.com/a/8767450/2114932
     query <- paste0(
-      "(SELECT nr, schemas[nr] AS table_schema FROM ",
-      "(SELECT *, generate_subscripts(schemas, 1) AS nr FROM ",
-      "(SELECT current_schemas(true) AS schemas) ",
-      "t) ",
-      "tt WHERE schemas[nr] <> 'pg_catalog') ",
-      "ttt"
+        "(",
+        "SELECT * FROM unnest(current_schemas(true)) WITH ORDINALITY AS tbl(table_schema, nr) \n",
+        "WHERE table_schema != 'pg_catalog'",
+        ") schemas_on_path"
     )
+    only_first <- TRUE
   }
 
-  table <- dbQuoteString(conn, id[["table"]])
+  # join columns info
+  table <- dbQuoteString(conn, name[["table"]])
   query <- paste0(
     query, " ",
-    "INNER JOIN INFORMATION_SCHEMA.", inf_table, " USING (table_schema) ",
+    "INNER JOIN INFORMATION_SCHEMA.COLUMNS USING (table_schema) ",
     "WHERE table_name = ", table
   )
 
   if (only_first) {
+    # we can only detect duplicate table names after we know in which schemas they are
     # https://stackoverflow.com/a/31814584/946850
     query <- paste0(
       "(SELECT *, rank() OVER (ORDER BY nr) AS rnr ",
@@ -185,7 +237,19 @@ find_table <- function(conn, id, inf_table = "tables", only_first = FALSE) {
     )
   }
 
-  query
+  query <- paste0(
+    "SELECT column_name FROM ",
+    query, " ",
+    "ORDER BY ordinal_position"
+  )
+
+  fields <- dbGetQuery(conn, query)[[1]]
+
+  if (length(fields) == 0) {
+    stop("Table ", dbQuoteIdentifier(conn, id), " not found.", call. = FALSE)
+  }
+
+  fields
 }
 
 find_temp_schema <- function(conn, fail_if_missing = TRUE) {
@@ -214,19 +278,3 @@ find_temp_schema <- function(conn, fail_if_missing = TRUE) {
     return(connection_get_temp_schema(conn@ptr))
   }
 }
-
-list_fields <- function(conn, id) {
-  name <- id@name
-
-  query <- find_table(conn, name, "columns", only_first = TRUE)
-  query <- paste0(
-    "SELECT column_name FROM ",
-    query, " ",
-    "ORDER BY ordinal_position"
-  )
-  fields <- dbGetQuery(conn, query)[[1]]
-  if (length(fields) == 0) {
-    stop("Table ", dbQuoteIdentifier(conn, name), " not found.", call. = FALSE)
-  }
-  fields
-}