Index: iknow-api/Data/PgEnumLabels.cs
===================================================================
--- iknow-api/Data/PgEnumLabels.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
+++ iknow-api/Data/PgEnumLabels.cs	(revision ea405569ef29f56fbfc4d77708b6b3faf9286097)
@@ -0,0 +1,49 @@
+using iknow_api.Models;
+using Npgsql;
+
+namespace iknow_api.Data
+{
+    /// <summary>
+    /// Maps CLR enum member names onto the labels declared in sql/ddl.sql.
+    /// Most labels are just the lowercased member name; the ones that are not
+    /// (UserRole.Professor -> 'prof', Grade.Ten -> '10') are listed explicitly.
+    ///
+    /// The instances are static on purpose. EF Core caches its internal service
+    /// provider against the DbContext options, and a fresh translator instance
+    /// on every resolution makes each set of options look different - EF then
+    /// builds a new provider per resolution and throws
+    /// ManyServiceProvidersCreatedWarning once it has built twenty.
+    /// </summary>
+    public sealed class PgEnumLabels : INpgsqlNameTranslator
+    {
+        public static readonly PgEnumLabels UserRole = new(
+            new Dictionary<string, string>
+            {
+                [nameof(Models.UserRole.Admin)] = "admin",
+                [nameof(Models.UserRole.Professor)] = "prof",
+                [nameof(Models.UserRole.Student)] = "student",
+            });
+
+        public static readonly PgEnumLabels Grade = new(
+            new Dictionary<string, string>
+            {
+                [nameof(Models.Grade.Six)] = "6",
+                [nameof(Models.Grade.Seven)] = "7",
+                [nameof(Models.Grade.Eight)] = "8",
+                [nameof(Models.Grade.Nine)] = "9",
+                [nameof(Models.Grade.Ten)] = "10",
+            });
+
+        /// <summary>Lowercases the member name, which is all the other enums need.</summary>
+        public static readonly PgEnumLabels Lowercase = new(new Dictionary<string, string>());
+
+        private readonly IReadOnlyDictionary<string, string> _labels;
+
+        private PgEnumLabels(IReadOnlyDictionary<string, string> labels) => _labels = labels;
+
+        public string TranslateTypeName(string clrName) => clrName;
+
+        public string TranslateMemberName(string clrName) =>
+            _labels.TryGetValue(clrName, out var label) ? label : clrName.ToLowerInvariant();
+    }
+}