fix(core): coerce string where values to match field types in adapter (#7860)

packages/better-auth/src/db/db.test.ts

@@ -97,6 +97,70 @@ describe("db", async () => {
 		expect(session?.user.email).toBe("test@email.com");
 	});
 
+	it("should coerce string where values to match field types", async () => {
+		// HTTP query params arrive as strings.
+		// The adapter should coerce values to match the field's schema type.
+		const { auth, db } = await getTestInstance(
+			{
+				user: {
+					additionalFields: {
+						age: { type: "number", required: false },
+					},
+				},
+			},
+			{
+				// Uses MongoDB because SQLite/MySQL/PostgreSQL silently cast types,
+				// which would make this test pass even without the coercion code.
+				testWith: "mongodb",
+			},
+		);
+
+		// boolean: "false" → false, "true" → true
+		const users = await db.findMany<{ emailVerified: boolean }>({
+			model: "user",
+			where: [{ field: "emailVerified", operator: "eq", value: "false" }],
+		});
+		expect(users.length).toBeGreaterThanOrEqual(1);
+		expect(users.every((u) => u.emailVerified === false)).toBe(true);
+
+		// number: "25" → 25
+		await db.update({
+			model: "user",
+			where: [{ field: "emailVerified", operator: "eq", value: false }],
+			update: { age: 25 },
+		});
+		const byAge = await db.findMany<{ age: number | null }>({
+			model: "user",
+			where: [{ field: "age", operator: "eq", value: "25" }],
+		});
+		expect(byAge.length).toBeGreaterThanOrEqual(1);
+		expect(byAge.every((u) => u.age === 25)).toBe(true);
+
+		// number array: ["25", "30"] → [25, 30]
+		await auth.api.signUpEmail({
+			body: {
+				email: "age30@test.com",
+				password: "password",
+				name: "user-30",
+				age: 30,
+			},
+		});
+		await auth.api.signUpEmail({
+			body: {
+				email: "age40@test.com",
+				password: "password",
+				name: "user-40",
+				age: 40,
+			},
+		});
+		const byAgeIn = await db.findMany<{ age: number | null }>({
+			model: "user",
+			where: [{ field: "age", operator: "in", value: ["25", "30"] }],
+		});
+		expect(byAgeIn).toHaveLength(2);
+		expect(byAgeIn.map((u) => u.age).sort()).toEqual([25, 30]);
+	});
+
 	it("delete hooks", async () => {
 		const hookUserDeleteBefore = vi.fn();
 		const hookUserDeleteAfter = vi.fn();

packages/core/src/db/adapter/factory.ts

@@ -540,12 +540,32 @@ export const createAdapterFactory =
 					newValue = value.toISOString();
 				}
 
+				if (fieldAttr.type === "boolean" && typeof newValue === "string") {
+					newValue = newValue === "true";
+				}
+
+				if (fieldAttr.type === "number") {
+					if (typeof newValue === "string" && newValue.trim() !== "") {
+						const parsed = Number(newValue);
+						if (!Number.isNaN(parsed)) {
+							newValue = parsed;
+						}
+					} else if (Array.isArray(newValue)) {
+						const parsed = newValue.map((v) =>
+							typeof v === "string" && v.trim() !== "" ? Number(v) : NaN,
+						);
+						if (parsed.every((n) => !Number.isNaN(n))) {
+							newValue = parsed;
+						}
+					}
+				}
+
 				if (
 					fieldAttr.type === "boolean" &&
-					typeof value === "boolean" &&
+					typeof newValue === "boolean" &&
 					!config.supportsBooleans
 				) {
-					newValue = value ? 1 : 0;
+					newValue = newValue ? 1 : 0;
 				}
 
 				if (