Merge pull request #3858 from crate/m/subcolumns-information-schema

CrateDB: display nested object as columns

docs/administration-guide/databases/cratedb.md

@@ -15,4 +15,8 @@ Starting in v0.18.0 Metabase provides a driver for connecting to CrateDB directl
 
 3. Click the `Save` button. Done.
 
-Metabase will now begin inspecting your CrateDB Dataset and finding any tables and fields to build up a sense for the schema. Give it a little bit of time to do its work and then you're all set to start querying.
\ No newline at end of file
+Metabase will now begin inspecting your CrateDB Dataset and finding any tables and fields to build up a sense for the schema. Give it a little bit of time to do its work and then you're all set to start querying.
+
+### Known limitations
+
+* Columns/Fields of type `object_array` are deactivated and not exposed. However, their nested fields are listed and also supported for queries.
\ No newline at end of file

src/metabase/driver/crate.clj

 (ns metabase.driver.crate
   (:require [clojure.java.jdbc :as jdbc]
+            [clojure.tools.logging :as log]
             [honeysql.core :as hsql]
             [metabase.driver :as driver]
             [metabase.driver.crate.util :as crate-util]
             [metabase.driver.generic-sql :as sql]
-            [metabase.util :as u]))
+            [metabase.util :as u])
+  (:import java.sql.DatabaseMetaData))
 
 (def ^:private ^:const column->base-type
   "Map of Crate column types -> Field base types
@@ -55,6 +57,39 @@
 (defn- string-length-fn [field-key]
   (hsql/call :char_length field-key))
 
+(defn- describe-table-fields
+  [database, driver, {:keys [schema name]}]
+  (let [columns (jdbc/query
+                  (sql/db->jdbc-connection-spec database)
+                  [(format "select column_name, data_type as type_name
+                            from information_schema.columns
+                            where table_name like '%s' and table_schema like '%s'
+                            and data_type != 'object_array'" name schema)])] ; clojure jdbc can't handle fields of type "object_array" atm
+    (set (for [{:keys [column_name type_name]} columns]
+           (merge {:name      column_name
+                   :custom    {:column-type type_name}
+                   :base-type (or (column->base-type (keyword type_name))
+                                  (do (log/warn (format "Don't know how to map column type '%s' to a Field base_type, falling back to :type/*." type_name))
+                                      :type/*))})))))
+
+(defn- add-table-pks
+  [^DatabaseMetaData metadata, table]
+  (let [pks (->> (.getPrimaryKeys metadata nil nil (:name table))
+                 jdbc/result-set-seq
+                 (mapv :column_name)
+                 set)]
+    (update table :fields (fn [fields]
+                            (set (for [field fields]
+                                   (if-not (contains? pks (:name field))
+                                     field
+                                     (assoc field :pk? true))))))))
+
+(defn- describe-table [driver database table]
+  (sql/with-metadata [metadata driver database]
+    (->> (describe-table-fields database driver table)
+         (assoc (select-keys table [:name :schema]) :fields)
+         ;; find PKs and mark them
+         (add-table-pks metadata))))
 
 (defrecord CrateDriver []
   clojure.lang.Named
@@ -65,6 +100,7 @@
   (merge (sql/IDriverSQLDefaultsMixin)
          {:can-connect?   (u/drop-first-arg can-connect?)
           :date-interval  crate-util/date-interval
+          :describe-table describe-table
           :details-fields (constantly [{:name         "hosts"
                                         :display-name "Hosts"
                                         :default      "localhost:5432"}])
@@ -75,6 +111,8 @@
           :column->base-type         (u/drop-first-arg column->base-type)
           :string-length-fn          (u/drop-first-arg string-length-fn)
           :date                      crate-util/date
+          :quote-style               (constantly :crate)
+          :field->alias              (constantly nil)
           :unix-timestamp->timestamp crate-util/unix-timestamp->timestamp
           :current-datetime-fn       (constantly now)}))
 

src/metabase/util/honeysql_extensions.clj

@@ -21,6 +21,23 @@
   (intern 'honeysql.format 'quote-fns
           (assoc quote-fns :h2 (comp s/upper-case ansi-quote-fn))))
 
+(defn- str-insert
+  "Insert c in string s at index i."
+  [s c i]
+  (str c (subs s 0 i) c (subs s i)))
+
+(defn- crate-column-identifier
+  [^CharSequence s]
+  (let [idx (s/index-of s "[")]
+    (if (nil? idx)
+      (str \" s \")
+      (str-insert s "\"" idx))))
+
+;; `:crate` quote style that correctly quotes nested column identifiers
+(let [quote-fns     @(resolve 'honeysql.format/quote-fns)]
+  (->> (assoc quote-fns :crate crate-column-identifier)
+       (intern 'honeysql.format 'quote-fns)))
+
 ;; register the `extract` function with HoneySQL
 ;; (hsql/format (hsql/call :extract :a :b)) -> "extract(a from b)"
 (defmethod hformat/fn-handler "extract" [_ unit expr]