正在渲染对象数组的数组，不断得到“警告：列表中的每个孩子都应该有一个唯一的“键”道具。

Question

I have an object that contains array of arrays. I was able to make it render the way I wanted. However, the React key is giving me trouble; throwing this "Warning: Each child in a list should have a unique "key" prop."

I have tried giving a unique 'id' property within the original array object for each element in each array but did not help.

I also looked through these but I think I have all of the suggestions there: Each child in an array or iterator should have a unique "key" prop in reactjs Warning: Each child in a list should have a unique "key" prop Warning: Each child in an array or iterator should have a unique "key" prop. Check the render method of `ListView`

My object

const courses = 
[
    {
      name: 'Half Stack application development',
      id: 'Half Stack application development',
      parts: [
        {
          name: 'Fundamentals of React',
          exercises: 10,
          id: 'Fundamentals of React'
        },
        {
          name: 'Using props to pass data',
          exercises: 7,
          id: 'Using props to pass data'
        },
        {
          name: 'State of a component',
          exercises: 14,
          id: 'State of a component'
        },
        {
          name: 'Redux',
          exercises: 11,
          id: 'Redux'
        }
      ]
    }, 
    {
      name: 'Node.js',
      id: 'Node.js',
      parts: [
        {
          name: 'Routing',
          exercises: 3,
          id: 'Routing'
        },
        {
          name: 'Middlewares',
          exercises: 7,
          id: 'Middlewares'
        }
        ]
    }
]


ReactDOM.render(<App course={courses}/>, document.getElementById('root'));

This is the callback order:

App -> Courses -> Course -> {Header, Content -> Part}

const App = ({course}) => {
  return (
    <>
      <Courses course={course} />
    </>
  )
}

const Courses = ({course}) => {
    console.log("Starting.....")
    const courseList = course.map(nameConent => nameConent)
    // console.log(courseList)
    // const idList = courseList.map(eachCourse =>eachCourse.id)
    const mapEverything = () => courseList.map(a => <Course name={a.name} partsList={a.parts} id={a.id}/>)
    // const mapEverything = () => courseList.map(a => console.log(a.id))
    // console.log("CourseID",idList)
    return (
        <>  
            {mapEverything()}
        </>

    )
}

const Course = ({name,partsList,id}) => {
    // console.log(name)
    console.log("CourseID", id)

    return (
        <>
            <div key={id}>
                <Header header={name} id={id}/>
                <Content contents={partsList} id={id+"======"}/>
            </div>
        </>
    )
}

const Content = ({contents,id}) => {
    console.log("contentsID",id)
    const partList = () => contents.map(part =>
        <Part
            name={part.name}
            id={part.id} 
            exercises={part.exercises}
        />
    )

    const getSumofArray = (accumulator, currentValue) => accumulator + currentValue

    const exeList = contents.map(content => content.exercises).reduce(getSumofArray)
    // console.log(exeList)
    return (
        <>
            <ul key={id}>
                {partList()}
            </ul>
            <b>total exercises: {exeList}</b>
        </>
    )
}

const Header = ({header, id}) => {
    console.log("HeaderID", id)
    return (
        <>
            <h1 key={id}>
                {header}
            </h1>
        </>
    )
}

const Part = ({name, id, exercises}) => {
    console.log("PartID", id)
    return (
        <>
            <li  key={id}>
                {name}: {exercises}
            </li>
        </>
    )
}

It's having trouble at the Courses and Content component.

screenshot of warnings: https://drive.google.com/open?id=1kcLlF0d90BG6LXPojDtfSlBFGafC9HC_

Answer 1

I think a problem is here:

const mapEverything = () => courseList.map(a => <Course name={a.name} partsList={a.parts} id={a.id}/>)

You should try add key here:

const mapEverything = () => courseList.map(a => <Course name={a.name} partsList={a.parts} id={a.id} key={a.id}/>)

And here too:

const partList = () => contents.map(part =>
        <Part
            name={part.name}
            id={part.id} 
            exercises={part.exercises}
            key={part.id}
        />)

Here is a good explanation of why you need to do it this way.