Migrate to yarn berry and fix all workspace errors

frontend/lib/dbConnect.js

@@ -0,0 +1,43 @@
+import mongoose from 'mongoose'
+
+const MONGODB_URI = process.env.MONGODB_URI
+
+if (!MONGODB_URI) {
+  throw new Error(
+    'Please define the MONGODB_URI environment variable inside .env.local'
+  )
+}
+
+/**
+ * Global is used here to maintain a cached connection across hot reloads
+ * in development. This prevents connections growing exponentially
+ * during API Route usage.
+ */
+let cached = global.mongoose
+
+if (!cached) {
+  cached = global.mongoose = { conn: null, promise: null }
+}
+
+async function dbConnect () {
+  if (cached.conn) {
+    return cached.conn
+  }
+
+  if (!cached.promise) {
+    const opts = {
+      useNewUrlParser: true,
+      useUnifiedTopology: true,
+      bufferCommands: false
+    }
+
+    cached.promise = mongoose.connect(MONGODB_URI, opts)
+      .then(mongoose => {
+        return mongoose
+      })
+  }
+  cached.conn = await cached.promise
+  return cached.conn
+}
+
+export default dbConnect