本來lightning-datatable這種標籤，基本上任何的專案都會用到而且很精通，所以當時感覺沒有太大的單獨一篇寫的必要，在Salesforce LWC學習(三十) lwc superbadge專案實現 中也有使用這個標籤的demo，所以有類似需要的小夥伴參考一下也可以照貓畫虎搞定需求。專案中遇見了兩個datatable的問題，解決以後感覺有必要寫一下，後期遇見這種坑的小夥伴可以快速對應。話不多說，先弄一個簡單的分頁效果的UI，UI很醜，旨在實現功能。

AccountListController.cls：一個簡單的搜尋list返回

public without sharing class AccountListController {
    public static final Integer DEFAULT_PAGE_SIZE = 100;
    @AuraEnabled(cacheable=false)
    public static List<Account> fetchAccountList(String serializedAccount){

        Account account = (Account)JSON.deserialize(serializedAccount,Account.class);
        String fetchAccountSQL = 'SELECT Id,Name,Industry,AccountSource,Owner.Name FROM Account WHERE IsDeleted = false ';

        if(String.isNotBlank(account.name)) {
            fetchAccountSQL += 'AND Name like' +  '\'%' + account.name + '%\'';
        }

        if(String.isNotBlank(account.industry)) {
            fetchAccountSQL += ' AND industry = \'' + account.industry + '\'';
        }

        if(String.isNotBlank(account.AccountSource)) {
            fetchAccountSQL += ' AND AccountSource = \'' + account.AccountSource + '\'';
        }

        Integer accountSize = DEFAULT_PAGE_SIZE;


        fetchAccountSQL += ' LIMIT ' + accountSize;
        List<Account> accountList = Database.query(fetchAccountSQL);
        return accountList;
    }
}

accountSearchForm.html

<template>
    <!--use LDS to bind account -->
    <lightning-record-edit-form
        object-api-name='Account'
        onsubmit={handleRecordFormSubmit}
    >
        <!--used to show section close/open-->
        <lightning-accordion allow-multiple-sections-open
            active-section-name={activeSections}>

            <lightning-accordion-section name="basic" label="basic">
                <lightning-layout multiple-rows="true">
                    <lightning-layout-item  padding="around-small" flexibility='auto' size='4'>
                        <lightning-input-field field-name='Name'></lightning-input-field>
                    </lightning-layout-item>

                    <lightning-layout-item padding="around-small" flexibility='auto' size='4'>
                        <lightning-input-field field-name="AccountSource"></lightning-input-field>
                    </lightning-layout-item>

                    <lightning-layout-item padding="around-small" flexibility='auto' size='4'>
                        <lightning-input-field field-name="Industry"></lightning-input-field>
                    </lightning-layout-item>
                </lightning-layout>
            </lightning-accordion-section>
        </lightning-accordion>

        <!-- button group area -->
        <lightning-layout horizontal-align="center">
            <lightning-layout-item >
                <lightning-button variant="brand" label="search" type="submit" name="search"></lightning-button>
            </lightning-layout-item>
        </lightning-layout>
    </lightning-record-edit-form>
</template>

accountSearchForm.js

import { LightningElement,track } from 'lwc';

export default class AccountSearchForm extends LightningElement {
    @track activeSections = ['basic'];

    @track account;

    handleRecordFormSubmit(event) {
        event.preventDefault();
        this.account = event.detail;
        this.dispatchEvent(new CustomEvent('searchaccount',{detail:this.account}));
    }

}

myAccountList.html

<template>
    <lightning-card title="list for account data" icon-name="standard:account">
        <div style="height: 150px;">
            <lightning-datatable
                data={accountListForCurrentPage}
                columns={columns}
                show-row-number-column
                key-field="id">
            </lightning-datatable>
        </div>

        <lightning-layout horizontal-align="center">
            <lightning-layout-item flexibility='auto' size='1'>
                <lightning-combobox
                    value={perSize}
                    options={entryList}
                    placeholder="choose size"
                    onchange={handlePerSizeChange} >

                </lightning-combobox>
            </lightning-layout-item>
            <lightning-layout-item flexibility='auto' size='9' class="slds-text-align_center">
                totalSize: {totalSize}
            </lightning-layout-item>
            <lightning-layout-item flexibility="auto" size="2">
                <lightning-button variant="brand" label="<--" disabled={isFirstPage} onclick={handlePreviousPageClick}></lightning-button>
                <lightning-button variant="brand" label="-->" disabled={isLastPage} title="next" onclick={handleNextPageClick}></lightning-button>
            </lightning-layout-item>
        </lightning-layout>
    </lightning-card>
</template>

myAccountList.js

import { LightningElement,api, track } from 'lwc';

const columns = [
    {label: 'Account Name', fieldName: 'Name'},
    {label: 'Account Industry', fieldName: 'Industry'},
    {label: 'Account Source', fieldName: 'AccountSource'},
    {label: 'Owner Name', fieldName: 'OwnerName'}
];

export default class MyAccountList extends LightningElement {
    //searched account list used to show in component table
    @api accountList;
    //indicator if table header checkbox check or not, true for check
    @api totalChecked;
    //list total entryList
    @api totalSize;
    //per size for show in table
    @api perSize;
    //current page index
    @api currentPageIndex;
    //list show in table
    @api accountListForCurrentPage;
    //indicator if current page is first page
    @api isFirstPage;
    //indicator if current page is last page
    @api isLastPage;

    @track columns = columns;

    get entryList() {
        return [
            { label: '3', value: '3' },
            { label: '5', value: '5' },
            { label: '10', value: '10' },
        ];
    }


    /**
     * description: item checkbox check/uncheck, dispatch itemcheck custom event and parent component handle this
     * @param event system event,used to get which item check/uncheck
     */
    handleItemCheckboxClick(event) {
        this.dispatchEvent(new CustomEvent('itemcheck',{detail:{id:event.currentTarget.value,checked:event.currentTarget.checked}}));
    }

    /**
     * description: table header checkbox check/check, dispatch allcheck custom event
     * @param  event system event, used to get if table header checkbox check/uncheck
     */
    handleAllCheckboxClick(event) {
        this.dispatchEvent(new CustomEvent('allcheck',{detail:{checked:event.currentTarget.checked}}));
    }

    handleNextPageClick() {
        this.dispatchEvent(new CustomEvent('nextpage'));
    }

    handlePreviousPageClick() {
        this.dispatchEvent(new CustomEvent('previouspage'));
    }

    handlePerSizeChange(event) {
        let currentSize = event.detail.value;
        this.dispatchEvent(new CustomEvent('persizechange',{detail:{currentSize:currentSize}}));
    }
}

accountListContainer.html

<template>
    <c-account-search-form onsearchaccount={handleSearchAccountEvent}></c-account-search-form>
    <c-my-account-list is-first-page={isFirstPage} is-last-page={isLastPage} account-list={accountList} account-list-for-current-page={accountListForCurrentPage} total-checked={totalChecked} onitemcheck={handleItemCheckEvent} onallcheck={handleAllCheckedEvent} onnextpage={handleNextPageEvent} onpreviouspage={handlePreviousPageEvent} total-size={totalSize} per-size={perSize} onpersizechange={handlePerSizeChangeEvent}></c-my-account-list>

</template>

accountListContainer.js

import { LightningElement,track } from 'lwc';
import fetchAccountList from '@salesforce/apex/AccountListController.fetchAccountList';

export default class AccountListContainer extends LightningElement {
    //account list used to show in account table
    @track accountList = [];
    //account form used to store form information user searched
    @track accountForm;
    //errors when fetch account list error
    @track errors;
    //indicator if table header total check box checked or not, true means checked
    @track totalChecked = false;
    //indicator if list modal close
    @track showSelectedListModal = false;

    @track data = [];

    //list total size
    @track totalSize;
    //per size for show in table
    @track perSize = 5;
    //current page index
    @track currentPageIndex;
    //list show in table
    @track accountListForCurrentPage;
    @track isFirstPage = true;
    @track isLastPage = true;

    /**
     * description: search account data by form information and set the result to account list to show in table
     * @param  event system event used to get form detail information
     */
    handleSearchAccountEvent(event) {
        this.totalChecked = false;
        this.accountForm = event.detail;
        fetchAccountList({serializedAccount:JSON.stringify(event.detail)})
            .then(result => {
                this.accountList = result;
                this.totalSize = result.length;
                this.currentPageIndex = 1;
                if(this.totalSize > this.perSize * this.currentPageIndex) {
                    this.setPagination();
                } else {
                    this.accountListForCurrentPage = this.accountList;
                    this.accountListForCurrentPage.forEach(item => {
                        if(item.Owner) {
                            item.OwnerName = item.Owner.Name;
                        }
                    });
                    this.isLastPage = true;
                }
                this.errors = undefined;
            })
            .catch(error =>{
                this.errors = error;
                this.accountList = undefined;
            });
    }

    handlePreviousPageEvent() {
        this.currentPageIndex = this.currentPageIndex - 1;
        this.setPagination();
    }

    handlePerSizeChangeEvent(event) {
        this.perSize = event.detail.currentSize;
        this.currentPageIndex = 1;
        this.setPagination();
    }

    handleNextPageEvent() {
        this.currentPageIndex = this.currentPageIndex + 1;
        this.setPagination();
    }


    setPagination() {
        this.accountListForCurrentPage = [];
        let tmpList = [];
        for(let index = (this.perSize * (this.currentPageIndex - 1)); index < this.totalSize; index++) {
            if(index < this.perSize * this.currentPageIndex) {
                if(this.accountList[index].Owner) {
                    this.accountList[index].OwnerName = this.accountList[index].Owner.Name;
                }
                tmpList.push(this.accountList[index]);
            }
        }
        this.accountListForCurrentPage = tmpList;
        if(this.currentPageIndex === 1) {
            this.isFirstPage = true;
        } else {
            this.isFirstPage = false;
        }
        if(this.perSize * this.currentPageIndex >= this.totalSize) {
            this.isLastPage = true;
        } else {
            this.isLastPage = false;
        }
    }
}

結果展示：

看上去還可以是吧，但是有兩個潛在的問題。

按照以下操作步驟，第一頁有拖動條，選擇了第5條資料

點選翻頁以後，兩個問題如下：

1）第二頁的第五條同樣的預設勾選了，儘管這個時候我們如果使用event.detail.selectedRows去獲取選中的選項，第二頁是沒有在這裡的，但是UI撒謊了，這個是一個很嚴重的bug；

2）第二頁進去以後，滾動條沒有在最上面，即沒有預設展示第一條資料。

這兩個問題，第二個問題是小問題，可以忍；第一個問題會讓使用者有concern，屬於很嚴重的問題。但是什麼原因呢？？？其實我也不太清楚是什麼原因，datatable官方的設計中也沒有翻頁的demo，大部分都是loadMore當頁增加資料場景，所以可能針對每頁的index處選中效果有某個隱藏的bug。當我們儘管更新了list的資料，但是index給渲染了，很容易是render層的bug。所以我們想一下如何去處理這種問題。既然同步的渲染有問題，我們考慮其他方式，setTimeout弄成非同步呼叫或者改成Promise實現。優化後的方案如下所示：

myAccountList.js新增一個方法

@api handleTableScrollTop() {
    this.template.querySelector('div').scrollTop = 0;
 }

accountListContainer.js修改一下 setPagination方法。新增了 setList這個Promise，js執行順序 ： 同步程式碼 > Promise > setTimeout這種非同步方式。

setPagination() {
        this.accountListForCurrentPage = [];
        let tmpList = [];
        for(let index = (this.perSize * (this.currentPageIndex - 1)); index < this.totalSize; index++) {
            if(index < this.perSize * this.currentPageIndex) {
                if(this.accountList[index].Owner) {
                    this.accountList[index].OwnerName = this.accountList[index].Owner.Name;
                }
                tmpList.push(this.accountList[index]);
            }
        }
        //this.accountListForCurrentPage = tmpList;
        if(this.currentPageIndex === 1) {
            this.isFirstPage = true;
        } else {
            this.isFirstPage = false;
        }
        if(this.perSize * this.currentPageIndex >= this.totalSize) {
            this.isLastPage = true;
        } else {
            this.isLastPage = false;
        }

        const setList = () =>
        new Promise((resolve, reject) => {
            resolve(tmpList);
        });

        setList()
        .then((result) => {
            this.accountListForCurrentPage = tmpList;
            this.template.querySelector('c-my-account-list').handleTableScrollTop();
        });
    }

 通過以上的程式碼就可以解決上述的兩個問題了。原理的話因為不清楚 datatable的渲染方式，只能找到解決這種問題的workaround的方式，同時作為sf開發人員在開發lightning的過程中，javascript真的是越來越重要了！！！

總結：篇中程式碼實現了通過 lightning-datatable翻頁效果以及針對兩個潛在的bug的修復。偏中有錯誤歡迎指出，有不懂歡迎留言。有更好方式歡迎交