尝试启动我的博客时出现错误

Question

我正在尝试使用express，mongoBD和node.js建立博客，但是我一直收到此错误。有人知道出什么事了吗？

我的错误：

(node:56513) UnhandledPromiseRejectionWarning: MongooseServerSelectionError: connect ECONNREFUSED 127.0.0.1:27017
    at NativeConnection.Connection.openUri (/Users/samanthamagrans/Desktop/magransWorld/node_modules/mongoose/lib/connection.js:827:32)
    at Mongoose.connect (/Users/samanthamagrans/Desktop/magransWorld/node_modules/mongoose/lib/index.js:335:15)
    at Object.<anonymous> (/Users/samanthamagrans/Desktop/magransWorld/server.js:6:10)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:831:12)
    at startup (internal/bootstrap/node.js:283:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:622:3)