跳到主要内容

findOne

查找符合条件的第一个实体，未找到返回 null。

方法签名​

findOne(options: FindOneOptions<T>): Observable<InstanceType<T> | null>

参数​

interface FindOneOptions<T> {
  where: RuleGroup<InstanceType<T>>;
  orderBy?: OrderBy[];
}

示例​

根据条件查找​

import { firstValueFrom } from 'rxjs';

const todo = await firstValueFrom(
  Todo.findOne({
    where: {
      combinator: 'and',
      rules: [{ field: 'id', operator: '=', value: '591e97aa-f7e3-499c-9fa4-4e2ae4459ef6' }]
    }
  })
);

if (todo) {
  console.log(todo.title);
}

查找最新记录​

const latest = await firstValueFrom(
  Todo.findOne({
    where: { combinator: 'and', rules: [] },
    orderBy: [{ field: 'createdAt', sort: 'desc' }]
  })
);

复杂条件​

const userTodo = await firstValueFrom(
  Todo.findOne({
    where: {
      combinator: 'and',
      rules: [
        { field: 'userId', operator: '=', value: 'user-123' },
        { field: 'completed', operator: '=', value: false }
      ]
    },
    orderBy: [
      { field: 'priority', sort: 'desc' },
      { field: 'createdAt', sort: 'asc' }
    ]
  })
);

组合复杂条件​

const urgentTodo = await firstValueFrom(
  Todo.findOne({
    where: {
      combinator: 'and',
      rules: [
        {
          field: 'completed',
          operator: '=',
          value: false
        },
        {
          combinator: 'or',
          rules: [
            {
              field: 'priority',
              operator: '=',
              value: 'high'
            },
            {
              field: 'dueDate',
              operator: '<',
              value: new Date()
            }
          ]
        }
      ]
    }
  })
);

在组件中使用​

import { Component, OnInit } from '@angular/core';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-todo-detail',
  template: `
    <div *ngIf="todo$ | async as todo; else notFound">
      <h2>{{ todo.title }}</h2>
      <p>{{ todo.description }}</p>
    </div>
    <ng-template #notFound>
      <p>未找到待办事项</p>
    </ng-template>
  `
})
export class TodoDetailComponent implements OnInit {
  @Input() todoId!: string;
  todo$!: Observable<Todo | null>;

  ngOnInit() {
    this.todo$ = Todo.findOne({
      where: {
        combinator: 'and',
        rules: [
          {
            field: 'id',
            operator: '=',
            value: this.todoId
          }
        ]
      }
    });
  }
}

findOne vs findOneOrFail​

方法未找到时行为返回类型使用场景
findOne返回 nullObservable<T | null>允许结果为空的查询
findOneOrFail抛出错误Observable<T>期望必定存在的查询
// findOne - 处理可能不存在的情况
const todo = await firstValueFrom(Todo.findOne({ where: { ... } }));
if (todo) {
  // 处理找到的情况
} else {
  // 处理未找到的情况
}

// findOneOrFail - 不存在时抛出错误
try {
  const todo = await firstValueFrom(Todo.findOneOrFail({ where: { ... } }));
  // 确定 todo 存在
} catch (error) {
  // 处理错误
}

性能优化建议​

1. 使用索引字段查询​

// ✅ 好：使用主键或索引字段
Todo.findOne({
  where: {
    combinator: 'and',
    rules: [{ field: 'id', operator: '=', value: 'xxx' }]
  }
});

// ⚠️ 慢：使用非索引字段
Todo.findOne({
  where: {
    combinator: 'and',
    rules: [{ field: 'description', operator: 'contains', value: 'keyword' }]
  }
});

2. 添加合适的 orderBy​

如果查询结果可能有多条，添加 orderBy 可以确保返回一致的结果：

Todo.findOne({
  where: {
    combinator: 'and',
    rules: [{ field: 'userId', operator: '=', value: 'user-123' }]
  },
  orderBy: [{ field: 'createdAt', sort: 'desc' }]
});

常见用例​

检查记录是否存在​

const exists = await firstValueFrom(
  Todo.findOne({
    where: {
      combinator: 'and',
      rules: [{ field: 'title', operator: '=', value: '重复的标题' }]
    }
  }).pipe(map(todo => !!todo))
);

获取默认值​

const todo = await firstValueFrom(
  Todo.findOne({
    where: {
      combinator: 'and',
      rules: [{ field: 'id', operator: '=', value: todoId }]
    }
  }).pipe(map(todo => todo ?? createDefaultTodo()))
);

参考​