arcgis for js 3.19从图层中读取和统计数据

阳光穿透心脏的1/2处 2024-04-19 08:48 54阅读 0赞

arcgis for js 3.19里面，从图层中读取和统计数据，主要使用 query、query task、StatisticDefinition。

query和task是什么关系？二者有什么区别？按我的理解，query负责定义查询语句、选项等等，相当于SQL语句；而task是查询引擎，负责将query付诸实施；StatisticDefinition好理解，就是统计。

上代码：

自定义查询控件query.Utils.js

define([
        "dojo/_base/declare",
        "esri/tasks/QueryTask",
        "esri/tasks/query",
    ], function (declare, QueryTask, Query) { 
        return declare("query.Utils", [], { 
            constructor: function () { 
    
            },
            executeQuery: function (opt, callback) { 
                var query = new Query();
                var task = new QueryTask(opt.url);
    
                for(var key in opt){ //查询选项
                    query[key] = opt[key];
                }
                if (!opt.outFields) { //默认返回所有字段
                    query.outFields = ["*"];
                }
                if(!opt.returnGeometry){ //默认不返回几何图形
                    opt.returnGeometry = false;
                }
    
                task.execute(query, callback);
            }
        });
    });

使用query.Utils.js

示例一

require([
        "toollib/query.Utils",
        "esri/tasks/StatisticDefinition"
    ], function (QueryUtils, StatisticDefinition) { 
        /* 综合本段代码，所起作用类似于 select count(位置分布) as num from 表 group by 位置分布; */
        let def = new StatisticDefinition();
        def.statisticType = "count";
        def.onStatisticField = "位置分布";
        def.outStatisticFieldName = "num";
    
        let queryUtil = new QueryUtils();
        queryUtil.executeQuery({ 
            url: layerurl,
            outStatistics: [def],
            groupByFieldsForStatistics:["位置分布"]
        }, function (data) { 
            let charts = { 
                category:[],
                series:[]
            };
            //组装数据
            for(var i in data.features){ 
                charts.category.push(data.features[i].attributes["位置分布"]);
                charts.series.push(data.features[i].attributes["num"]);
            }
            //展示数据
            ……
        });
    });

示例二

require([
        "toollib/query.Utils",
        "esri/tasks/StatisticDefinition"
    ], function (QueryUtils, StatisticDefinition) { 
    
        let queryUtil = new QueryUtils();
        queryUtil.executeQuery({ 
            url: 图层地址,
            where: "1=1",
            orderByFields: ["分类"],//使用“分类”这个字段进行排序。降序可以用["X desc","Y desc"]
            outFields: ["猴子分布区域名称","经度","纬度","分类"]
        }, function (data) { 
            let tableData = { 
                unit: [],
                x:[],
                y:[]
            };
            //获取数据
            for (var i in data.features) { 
                tableData.unit.push(data.features[i].attributes["猴子分布区域名称"]);
                tableData.x.push(data.features[i].attributes["经度"]);
                tableData.y.push(data.features[i].attributes["纬度"]);
            }
            //展示数据
            ……
        });
    });