[英]Error Handling For Undefined From Subscription - Apollo and Angular 2
我在Angular 2中使用Apollo查询GraphQL端点有以下代码:
getStudentPersonalDetails(studentId?: number) {
console.log(studentId)
this.apollo.watchQuery<QueryResponse>({
query: StudentPersonalDetailsQ,
variables: {
studentId: studentId
}
}).subscribe(({ data }) => {
if (typeof data.allStudentDetails != 'undefined') {
console.log(data)
this.loading = data.loading;
this.personalDetails.studentId = data.allStudentDetails.nodes[0].studentPk;
this.personalDetails.firstName = data.allStudentDetails.nodes[0].firstName;
this.personalDetails.middleName = data.allStudentDetails.nodes[0].middleName;
this.personalDetails.lastName = data.allStudentDetails.nodes[0].lastName;
this.personalDetails.preferredName = data.allStudentDetails.nodes[0].preferredName;
this.personalDetails.onlyOneName = data.allStudentDetails.nodes[0].onlyOneName;
this.personalDetails.dob = data.allStudentDetails.nodes[0].dob;
this.personalDetails.sex = data.allStudentDetails.nodes[0].sex;
this.personalDetails.birthCountry = data.allStudentDetails.nodes[0].metaCountryByBirthCountryId.countryName;
this.personalDetails.passportCountry = data.allStudentDetails.nodes[0].metaCountryByPassportCountryId.countryName;
this.personalDetails.passportNumber = data.allStudentDetails.nodes[0].passportNumber;
this.personalDetails.contactCountry = data.allStudentDetails.nodes[0].metaCountryByContactCountryId.countryName;
this.personalDetails.personalEmail = data.allStudentDetails.nodes[0].personalEmail;
console.log(data.allStudentDetails);
}
}, (error) => {
console.log('there was an error sending the query', error);
});
我通过有意传递不存在的学生ID并因此返回Cannot read property 'studentPk' of undefined
测试该方法。 但是,我试图通过检测allStudentDetails
是否未定义并转移到错误捕获来避免此错误。
如何添加错误处理以处理undefined
数据,然后适当地将其从服务中馈送到将使用烤面包机显示用户友好错误的组件?
如果我理解这个问题,则可以先通过map
运行响应,然后在该级别抛出错误。 类似于(当然这未经测试):
getStudentPersonalDetails(studentId?: number) {
console.log(studentId)
this.apollo.watchQuery<QueryResponse>({
query: StudentPersonalDetailsQ,
variables: {
studentId: studentId
}
}).map((data) => {
console.log(data.allStudentDetails);
if (typeof data.allStudentDetails.nodes[0] === 'undefined') {
// Could also check if array length is 0
// data.allStudentDetails.nodes.length <= 0
throw new Error('This student does not exist!');
}
return data;
}).subscribe((data) => {
console.log(data)
this.loading = data.loading;
this.personalDetails.studentId = data.allStudentDetails.nodes[0].studentPk;
this.personalDetails.firstName = data.allStudentDetails.nodes[0].firstName;
this.personalDetails.middleName = data.allStudentDetails.nodes[0].middleName;
this.personalDetails.lastName = data.allStudentDetails.nodes[0].lastName;
this.personalDetails.preferredName = data.allStudentDetails.nodes[0].preferredName;
this.personalDetails.onlyOneName = data.allStudentDetails.nodes[0].onlyOneName;
this.personalDetails.dob = data.allStudentDetails.nodes[0].dob;
this.personalDetails.sex = data.allStudentDetails.nodes[0].sex;
this.personalDetails.birthCountry = data.allStudentDetails.nodes[0].metaCountryByBirthCountryId.countryName;
this.personalDetails.passportCountry = data.allStudentDetails.nodes[0].metaCountryByPassportCountryId.countryName;
this.personalDetails.passportNumber = data.allStudentDetails.nodes[0].passportNumber;
this.personalDetails.contactCountry = data.allStudentDetails.nodes[0].metaCountryByContactCountryId.countryName;
this.personalDetails.personalEmail = data.allStudentDetails.nodes[0].personalEmail;
}, (error) => {
console.log(error.message);
});
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