app2-api/modules/comments/comment.model.js

module.exports = function (sequelize, DataTypes) {
    const Comment = sequelize.define('Comment', {
        id: {
            type: DataTypes.UUID,
            defaultValue: DataTypes.UUIDV4,
            primaryKey: true
        },
        entityId: {
            type: DataTypes.UUID,
            allowNull: false,
        },
        entityName: {
            type: DataTypes.STRING,
            allowNull: false,
        },
        type: {
            type: DataTypes.STRING,
            allowNull: false,
        },
        content: {
            type: DataTypes.STRING,
            allowNull: false
        },
        entity: {
            type: DataTypes.VIRTUAL,
            get: function () {
                const name = this.get('entityName');
                const id = this.get('entityId');
                let modelName = '';
                switch (name) {
                    case 'post':
                        modelName = 'Post';
                        break;
                    case 'speaker':
                        modelName = 'Speaker'
                        break;

                    case 'event':
                        modelName = 'Event';
                        break;

                    default:
                        break;
                }

                return sequelize.models[modelName].findOne(id);
            }
        }
    }, {
            indexes: [{
                unique: false,
                fields: ['entityId']
            }],
            tableName: 'comments',
            freezeTableName: true,
            timestamps: true,
        });


    Comment.associate = function (models) {
        Comment.User = Comment.belongsTo(models.User, { foreignKey: 'userId', constraints: false });
        //Comment.Conference = Comment.belongsTo(models.Conference, { foreignKey: 'conferenceId', constraints: false });
        //Comment.Post = Comment.belongsTo(models.Post, { foreignKey: 'postId', constraints: false });
        //Comment.Speaker = Comment.belongsTo(models.Speaker, { foreignKey: 'speakerId', constraints: false });
    };

    return Comment;

};