From fd7256014beb9ee2da225e26e6bce5ef2c0f7761 Mon Sep 17 00:00:00 2001
From: Dylan Vanmali <dvanmali@users.noreply.github.com>
Date: Tue, 2 Dec 2025 10:24:22 -0800
Subject: [PATCH] fix(db-adapter): string[] and number[] fieldTypes incorrectly
 parsed for plugins (#4237)

---
 .../src/adapters/adapter-factory/index.ts     | 13 ++++
 .../test/adapter-factory.test.ts              | 76 +++++++++++++++++++
 2 files changed, 89 insertions(+)

diff --git a/packages/better-auth/src/adapters/adapter-factory/index.ts b/packages/better-auth/src/adapters/adapter-factory/index.ts
index 978d9f87bd..3cc703af54 100644
--- a/packages/better-auth/src/adapters/adapter-factory/index.ts
+++ b/packages/better-auth/src/adapters/adapter-factory/index.ts
@@ -247,6 +247,13 @@ export const createAdapterFactory =
 					fieldAttributes!.type === "json"
 				) {
 					newValue = JSON.stringify(newValue);
+				} else if (
+					config.supportsJSON === false &&
+					Array.isArray(newValue) &&
+					(fieldAttributes!.type === "string[]" ||
+						fieldAttributes!.type === "number[]")
+				) {
+					newValue = JSON.stringify(newValue);
 				} else if (
 					config.supportsDates === false &&
 					newValue instanceof Date &&
@@ -335,6 +342,12 @@ export const createAdapterFactory =
 							field.type === "json"
 						) {
 							newValue = safeJSONParse(newValue);
+						} else if (
+							config.supportsJSON === false &&
+							typeof newValue === "string" &&
+							(field.type === "string[]" || field.type === "number[]")
+						) {
+							newValue = safeJSONParse(newValue);
 						} else if (
 							config.supportsDates === false &&
 							typeof newValue === "string" &&
diff --git a/packages/better-auth/src/adapters/adapter-factory/test/adapter-factory.test.ts b/packages/better-auth/src/adapters/adapter-factory/test/adapter-factory.test.ts
index 71a8f5b444..672cbf1176 100644
--- a/packages/better-auth/src/adapters/adapter-factory/test/adapter-factory.test.ts
+++ b/packages/better-auth/src/adapters/adapter-factory/test/adapter-factory.test.ts
@@ -522,6 +522,82 @@ describe("Create Adapter Helper", async () => {
 				expect(createFALSEParameters.data.emailVerified).toBe(0);
 			});
 
+			test("Should modify string[] type to TEXT if the DB doesn't support it. And expect the result to be transformed back to string[]", async () => {
+				const createJSONParameters: { data: { preferences: string } } =
+					await new Promise(async (r) => {
+						const adapter = await createTestAdapter({
+							config: {
+								supportsJSON: false,
+							},
+							options: {
+								user: {
+									additionalFields: {
+										preferences: {
+											type: "string[]",
+										},
+									},
+								},
+							},
+							adapter(args_0) {
+								return {
+									async create(data) {
+										r(data as any);
+										return data.data;
+									},
+								};
+							},
+						});
+						const obj = { preferences: ["medium", "large"] };
+						const res = await adapter.create({
+							model: "user",
+							data: obj,
+						});
+						expect(res).toHaveProperty("preferences");
+						expect(res.preferences).toEqual(obj.preferences);
+					});
+				expect(createJSONParameters.data).toHaveProperty("preferences");
+				expect(createJSONParameters.data.preferences).toEqual(
+					'[\"medium\",\"large\"]',
+				);
+			});
+
+			test("Should modify number[] type to TEXT if the DB doesn't support it. And expect the result to be transformed back to number[]", async () => {
+				const createJSONParameters: { data: { preferences: string } } =
+					await new Promise(async (r) => {
+						const adapter = await createTestAdapter({
+							config: {
+								supportsJSON: false,
+							},
+							options: {
+								user: {
+									additionalFields: {
+										preferences: {
+											type: "number[]",
+										},
+									},
+								},
+							},
+							adapter(args_0) {
+								return {
+									async create(data) {
+										r(data as any);
+										return data.data;
+									},
+								};
+							},
+						});
+						const obj = { preferences: [6, 7] };
+						const res = await adapter.create({
+							model: "user",
+							data: obj,
+						});
+						expect(res).toHaveProperty("preferences");
+						expect(res.preferences).toEqual(obj.preferences);
+					});
+				expect(createJSONParameters.data).toHaveProperty("preferences");
+				expect(createJSONParameters.data.preferences).toEqual("[6,7]");
+			});
+
 			test("Should modify JSON type to TEXT if the DB doesn't support it. And expect the result to be transformed back to JSON", async () => {
 				const createJSONParameters: { data: { preferences: string } } =
 					await new Promise(async (r) => {