create attachment file table

backend/models/caseAttachments.js

@@ -0,0 +1,27 @@
+function defineCaseAttachment(sequelize, DataTypes) {
+  const CaseAttachment = sequelize.define("CaseAttachment", {
+    caseId: {
+      type: DataTypes.INTEGER,
+      allowNull: false,
+    },
+    attachmentId: {
+      type: DataTypes.INTEGER,
+      allowNull: false,
+    },
+  });
+
+  CaseAttachment.associate = (models) => {
+    CaseAttachment.belongsTo(models.Case, {
+      foreignKey: "caseId",
+      onDelete: "CASCADE",
+    });
+    CaseAttachment.belongsTo(models.Attachment, {
+      foreignKey: "attachmentId",
+      onDelete: "CASCADE",
+    });
+  };
+
+  return CaseAttachment;
+}
+
+module.exports = defineCaseAttachment;