diff --git a/app/db/migrations/versions/20faa9f18c0a_init.py b/app/db/migrations/versions/20faa9f18c0a_init.py
index 5f4f674..d4e71e3 100644
--- a/app/db/migrations/versions/20faa9f18c0a_init.py
+++ b/app/db/migrations/versions/20faa9f18c0a_init.py
@@ -46,7 +46,7 @@ def upgrade() -> None:
         sa.Column("name", sa.String(length=256), nullable=True),
         sa.Column("address", sa.String(length=256), nullable=True),
         sa.Column("port", sa.Integer(), nullable=True),
-        sa.Column("connection_backend", sa.String(), nullable=True),
+        sa.Column("connection_backend", sa.String(32), nullable=True),
         sa.Column("xray_version", sa.String(length=32), nullable=True),
         sa.Column(
             "status",
@@ -115,7 +115,7 @@ def upgrade() -> None:
             nullable=True,
         ),
         sa.Column("tag", sa.String(length=256), nullable=False),
-        sa.Column("config", sa.String(), nullable=False),
+        sa.Column("config", sa.String(512), nullable=False),
         sa.Column("node_id", sa.Integer(), nullable=True),
         sa.ForeignKeyConstraint(
             ["node_id"],
@@ -164,7 +164,7 @@ def upgrade() -> None:
             nullable=False,
         ),
         sa.Column("ip_limit", sa.Integer(), nullable=False),
-        sa.Column("settings", sa.String(), nullable=True),
+        sa.Column("settings", sa.String(1024), nullable=True),
         sa.Column("expire", sa.DateTime(), nullable=True),
         sa.Column("admin_id", sa.Integer(), nullable=True),
         sa.Column("sub_updated_at", sa.DateTime(), nullable=True),
diff --git a/app/db/models.py b/app/db/models.py
index 4863c77..7c80bad 100644
--- a/app/db/models.py
+++ b/app/db/models.py
@@ -108,7 +108,7 @@ class User(Base):
         default=UserDataLimitResetStrategy.no_reset,
     )
     ip_limit = Column(Integer, nullable=False, default=-1)
-    settings = Column(String)
+    settings = Column(String(1024))
     usage_logs = relationship(
         "UserUsageResetLogs", back_populates="user", lazy="joined"
     )
@@ -153,7 +153,7 @@ class Inbound(Base):
     id = Column(Integer, primary_key=True)
     protocol = Column(Enum(ProxyTypes))
     tag = Column(String(256), nullable=False)
-    config = Column(String(), nullable=False)
+    config = Column(String(512), nullable=False)
     node_id = Column(Integer, ForeignKey("nodes.id"), index=True)
     node = relationship("Node", back_populates="inbounds")
     services = relationship(
@@ -228,7 +228,7 @@ class Node(Base):
     __table_args__ = (UniqueConstraint("address", "port"),)
     id = Column(Integer, primary_key=True)
     name = Column(String(256), unique=True)
-    connection_backend = Column(String())
+    connection_backend = Column(String(32))
     address = Column(String(256))
     port = Column(Integer)
     xray_version = Column(String(32))