Mongo Plugin works here. Barring the scenarios where the query json contains special characters in keys ($, .) it works properly.

app/server/appsmith-interfaces/src/main/java/com/appsmith/external/models/ActionConfiguration.java

@@ -35,7 +35,16 @@ public class ActionConfiguration {
     HttpMethod httpMethod;
 
     // DB action fields
-    String query;
+
+    /*
+     * For SQL plugins, the query field would be of the following format :
+     * {
+     *     "cmd" : "select * from users;"
+     * }
+     * For noSQL plugins, the query json would be constructed according to
+     * the requirements of the plugin.
+     */
+    Map<String, Object> query;
 
     /*
      * Future plugins could require more fields that are not covered above.

app/server/appsmith-interfaces/src/main/java/com/appsmith/external/models/ResourceConfiguration.java

@@ -23,4 +23,9 @@ public class ResourceConfiguration {
 
     //For REST API
     List<Property> headers;
+
+    //This field is for plugins which allow the database name to be specified outside of the connection URL. The
+    //expectation from the plugins is that if the database name has been provided via this field, the database name
+    //should be according to this, else if database name is null, pick the database name from the URL.
+    String databaseName;
 }

app/server/appsmith-plugins/mongoPlugin/pom.xml

@@ -0,0 +1,84 @@
+<?xml version="1.0" encoding="UTF-8"?>
+
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>com.external.plugins</groupId>
+    <artifactId>mongoPlugin</artifactId>
+    <version>1.0-SNAPSHOT</version>
+
+    <name>mongoPlugin</name>
+
+    <properties>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <java.version>11</java.version>
+        <maven.compiler.source>${java.version}</maven.compiler.source>
+        <maven.compiler.target>${java.version}</maven.compiler.target>
+        <plugin.id>mongo-plugin</plugin.id>
+        <plugin.class>com.external.plugins.MongoPlugin</plugin.class>
+        <plugin.version>1.0-SNAPSHOT</plugin.version>
+        <plugin.provider>tech@appsmith.com</plugin.provider>
+        <plugin.dependencies/>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>4.11</version>
+            <scope>test</scope>
+        </dependency>
+
+        <dependency>
+            <groupId>org.pf4j</groupId>
+            <artifactId>pf4j-spring</artifactId>
+            <version>0.5.0</version>
+        </dependency>
+
+        <dependency>
+            <groupId>com.appsmith</groupId>
+            <artifactId>interfaces</artifactId>
+            <version>1.0-SNAPSHOT</version>
+        </dependency>
+
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.18.8</version>
+            <scope>provided</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.mongodb</groupId>
+            <artifactId>mongo-java-driver</artifactId>
+            <version>3.11.1</version>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.1</version>
+            </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.1.2</version>
+                <configuration>
+                    <archive>
+                        <manifestEntries>
+                            <Plugin-Id>${plugin.id}</Plugin-Id>
+                            <Plugin-Class>${plugin.class}</Plugin-Class>
+                            <Plugin-Version>${plugin.version}</Plugin-Version>
+                            <Plugin-Provider>${plugin.provider}</Plugin-Provider>
+                            <Plugin-Dependencies>${plugin.dependencies}</Plugin-Dependencies>
+                        </manifestEntries>
+                    </archive>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

app/server/appsmith-plugins/mongoPlugin/src/main/java/com/external/plugins/MongoPlugin.java

@@ -0,0 +1,130 @@
+package com.external.plugins;
+
+import com.appsmith.external.models.ActionConfiguration;
+import com.appsmith.external.models.ActionExecutionResult;
+import com.appsmith.external.models.ResourceConfiguration;
+import com.appsmith.external.plugins.BasePlugin;
+import com.appsmith.external.plugins.PluginExecutor;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.mongodb.MongoClient;
+import com.mongodb.MongoClientURI;
+import com.mongodb.client.MongoDatabase;
+import lombok.extern.slf4j.Slf4j;
+import org.bson.Document;
+import org.bson.conversions.Bson;
+import org.json.JSONArray;
+import org.json.JSONObject;
+import org.pf4j.Extension;
+import org.pf4j.PluginWrapper;
+import reactor.core.publisher.Mono;
+
+import java.math.BigInteger;
+
+@Slf4j
+public class MongoPlugin extends BasePlugin {
+
+    private static ObjectMapper objectMapper;
+
+    public MongoPlugin(PluginWrapper wrapper) {
+        super(wrapper);
+        this.objectMapper = new ObjectMapper();
+    }
+
+    @Slf4j
+    @Extension
+    public static class MongoPluginExecutor implements PluginExecutor {
+
+        /**
+         * For reference on creating the json queries for Mongo please head to
+         * https://docs.huihoo.com/mongodb/3.4/reference/command/index.html
+         *
+         * @param connection : This is the connection that is established to the data source. This connection is according
+         *                   to the parameters in Resource Configuration
+         * @param resourceConfiguration : These are the configurations which have been used to create a Resource from a Plugin
+         * @param actionConfiguration : These are the configurations which have been used to create an Action from a Resource.
+         * @return
+         */
+        @Override
+        public Mono<ActionExecutionResult> execute(Object connection,
+                                                   ResourceConfiguration resourceConfiguration,
+                                                   ActionConfiguration actionConfiguration) {
+
+            ActionExecutionResult result = new ActionExecutionResult();
+            MongoClient mongoClient = (MongoClient) connection;
+            if (mongoClient == null) {
+                return Mono.error(new Exception("Mongo Client is null."));
+            }
+
+            MongoClientURI mongoClientURI= new MongoClientURI(resourceConfiguration.getUrl());
+
+            String databaseName = resourceConfiguration.getDatabaseName();
+            if (databaseName == null) {
+                databaseName = mongoClientURI.getDatabase();
+            }
+
+            MongoDatabase database = mongoClient.getDatabase(databaseName);
+
+            Bson command = new Document(actionConfiguration.getQuery());
+
+            try {
+
+                Document mongoOutput = database.runCommand(command);
+
+                JSONObject outputJson = new JSONObject(mongoOutput.toJson());
+                //The output json contains the key "ok". This is the status of the command
+                BigInteger status = outputJson.getBigInteger("ok");
+                JSONArray headerArray = new JSONArray();
+                if (BigInteger.ONE == status) {
+                    //The json contains key "cursor" when find command was issued and there are 1 or more results. In case
+                    //there are no results for find, this key is not present in the result json.
+                    if (outputJson.has("cursor")) {
+                        JSONArray outputResult = outputJson.getJSONObject("cursor").getJSONArray("firstBatch");
+                        result.setBody(objectMapper.readTree(outputResult.toString()));
+                    }
+                    //The json contains key "n" when insert/update command is issued. "n" for update signifies the no of
+                    //documents selected for update. "n" in case of insert signifies the number of documents inserted.
+                    if (outputJson.has("n")) {
+                        JSONObject body = new JSONObject().put("n", outputJson.getBigInteger("n"));
+                        headerArray.put(body);
+                    }
+                    //The json key constains key "nModified" in case of update command. This signifies the no of
+                    //documents updated.
+                    if (outputJson.has("nModified")) {
+                        JSONObject body = new JSONObject().put("nModified", outputJson.getBigInteger("nModified"));
+                        headerArray.put(body);
+                    }
+
+                    /** TODO
+                     * Go through all the possible fields that are returned in the output JSON and add all the fields
+                     * that are important to the headerArray.
+                     */
+                }
+
+                JSONObject statusJson = new JSONObject().put("ok", status);
+                headerArray.put(statusJson);
+                result.setHeaders(objectMapper.readTree(headerArray.toString()));
+            } catch (Exception e) {
+                return Mono.error(e);
+            }
+
+            return Mono.just(result);
+        }
+
+        @Override
+        public Object resourceCreate(ResourceConfiguration resourceConfiguration) {
+
+            MongoClientURI mongoClientURI= new MongoClientURI(resourceConfiguration.getUrl());
+            return new MongoClient(mongoClientURI);
+        }
+
+        @Override
+        public void resourceDestroy(Object connection) {
+            MongoClient mongoClient = (MongoClient) connection;
+            if (mongoClient != null) {
+                mongoClient.close();
+            }
+        }
+
+    }
+
+}

app/server/appsmith-plugins/mongoPlugin/src/test/java/com/external/plugins/MongoPluginTest.java

@@ -0,0 +1,18 @@
+package com.external.plugins;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit test for simple App.
+ */
+public class MongoPluginTest {
+    /**
+     * Rigorous Test :-)
+     */
+    @Test
+    public void shouldAnswerWithTrue() {
+        assertTrue(true);
+    }
+}

app/server/appsmith-plugins/pom.xml

@@ -17,6 +17,7 @@
     <modules>
         <module>postgresPlugin</module>
         <module>restApiPlugin</module>
+        <module>mongoPlugin</module>
     </modules>
 
 </project>

app/server/appsmith-plugins/postgresPlugin/src/main/java/com/external/plugins/PostgresPlugin.java

@@ -2,14 +2,11 @@ package com.external.plugins;
 
 import com.appsmith.external.models.ActionConfiguration;
 import com.appsmith.external.models.ActionExecutionResult;
-import com.appsmith.external.models.Param;
 import com.appsmith.external.models.ResourceConfiguration;
 import com.appsmith.external.plugins.BasePlugin;
 import com.appsmith.external.plugins.PluginExecutor;
-import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import lombok.extern.slf4j.Slf4j;
-import org.json.JSONObject;
 import org.pf4j.Extension;
 import org.pf4j.PluginException;
 import org.pf4j.PluginWrapper;
@@ -24,7 +21,7 @@ import java.sql.SQLException;
 import java.sql.Statement;
 import java.util.ArrayList;
 import java.util.HashMap;
-import java.util.List;
+import java.util.Map;
 
 @Slf4j
 public class PostgresPlugin extends BasePlugin {
@@ -38,6 +35,13 @@ public class PostgresPlugin extends BasePlugin {
         this.objectMapper = new ObjectMapper();
     }
 
+    /**
+     * Postgres plugin receives the query as json of the following format :
+     * {
+     *     "cmd" : "select * from users;"
+     * }
+     */
+
     @Slf4j
     @Extension
     public static class PostgresPluginExecutor implements PluginExecutor {
@@ -53,8 +57,9 @@ public class PostgresPlugin extends BasePlugin {
             ArrayList list = new ArrayList(50);
             try {
                 Statement statement = conn.createStatement();
-
+                Map<String, Object> queryJson = actionConfiguration.getQuery();
-                ResultSet resultSet = statement.executeQuery(actionConfiguration.getQuery());
+                String query = (String) queryJson.get("cmd");
+                ResultSet resultSet = statement.executeQuery(query);
                 ResultSetMetaData metaData = resultSet.getMetaData();
                 Integer colCount = metaData.getColumnCount();
                 while (resultSet.next()) {
@@ -90,7 +95,8 @@ public class PostgresPlugin extends BasePlugin {
             } catch (SQLException e) {
                 log.error("", e);
             }
-            return conn;
+            // Connection wasn't created. Return null
+            return null;
         }
 
         @Override

app/server/appsmith-server/src/main/java/com/appsmith/server/exceptions/AppsmithError.java

@@ -18,7 +18,8 @@ public enum AppsmithError {
     UNAUTHORIZED_ACCESS(401, 4002, "Unauthorized access"),
     INTERNAL_SERVER_ERROR(500, 5000, "Internal server error while processing request"),
     REPOSITORY_SAVE_FAILED(500, 5001, "Repository save failed."),
-    PLUGIN_INSTALLATION_FAILED_DOWNLOAD_ERROR(500, 5002, "Due to error in downloading the plugin from remote repository, plugin installation has failed. Check the jar location and try again.");
+    PLUGIN_INSTALLATION_FAILED_DOWNLOAD_ERROR(500, 5002, "Due to error in downloading the plugin from remote repository, plugin installation has failed. Check the jar location and try again."),
+    PLUGIN_RUN_FAILED(500, 5003, "Plugin execution failed with error {0}");
 
 
     private Integer httpErrorCode;

app/server/appsmith-server/src/main/java/com/appsmith/server/services/ActionServiceImpl.java

@@ -10,7 +10,6 @@ import com.appsmith.server.domains.Page;
 import com.appsmith.server.domains.PageAction;
 import com.appsmith.server.domains.Plugin;
 import com.appsmith.server.domains.Resource;
-import com.appsmith.server.domains.ResourceContext;
 import com.appsmith.server.domains.User;
 import com.appsmith.server.dtos.ExecuteActionDTO;
 import com.appsmith.server.exceptions.AppsmithError;
@@ -171,15 +170,15 @@ public class ActionServiceImpl extends BaseService<ActionRepository, Action, Str
                             resourceConfiguration = resource.getResourceConfiguration();
                             actionConfiguration = action.getActionConfiguration();
                         }
-
                         return resourceContextService
                                     .getResourceContext(resource.getId())
-                                //Now that we have the context (connection details, execute the action
+                                    //Now that we have the context (connection details, execute the action
                                     .flatMap(resourceContext -> pluginExecutor.execute(
                                                                                   resourceContext.getConnection(),
                                                                                   resourceConfiguration,
                                                                                   actionConfiguration));
                     }))
+                    .onErrorResume(e -> Mono.error(new AppsmithException(AppsmithError.PLUGIN_RUN_FAILED, e.getMessage())))
                     .flatMap(obj -> obj);
     }
 

app/server/appsmith-server/src/main/resources/public/appsmith/authz/acl.rego

@@ -13,6 +13,9 @@ url_allow = true {
     p = op.permission
 }
 
+# This is a global list of all the routes for all controllers. Any new controller that is written must
+# carry an entry in this array. OPA performs ACL based on an intersection of these entries and permissions
+# for a user + permissions inherited via the groups that the user is a part of.
 allowed_operations = [
     {"method": "POST", "resource": "users", "permission": "create:users"},
     {"method": "GET", "resource": "users", "permission": "read:users"},