# JsonReader.js

    /**
     * @class Ext.data.JsonReader
     * @extends Ext.data.DataReader
     * Data reader class to create an Array of Ext.data.Record objects from a JSON response
     * based on mappings in a provided Ext.data.Record constructor.
     * <p>
     * The code below lists all configuration options.
     * <pre><code>
       var RecordDef = Ext.data.Record.create([
           {name: 'name', mapping: 'name'},     // "mapping" property not needed if it's the same as "name"
           {name: 'occupation'},                // This field will use "occupation" as the mapping.
       ]);
       var myReader = new Ext.data.JsonReader({
           totalProperty: "results",    // The property which contains the number of returned records (optional)
           root: "rows",                // The property which contains an Array of record objects
           id: "id"                     // The property within the record object that provides an ID for the record (optional)
       }, RecordDef);
      </code></pre>
     * <p>
     * This would consume a JSON file like this:
     * <pre><code>
       { 'results': 2, 'rows': [
         { 'id': 1, 'name': 'Bill', occupation: 'Gardener' },
         { 'id': 2, 'name': 'Ben', occupation: 'Horticulturalist' } ]
       }
      </code></pre>
     * @cfg {String} totalProperty Name of the property from which to retrieve the total number of records
     * in the dataset. This is only needed if the whole dataset is not passed in one go, but is being
     * paged from the remote server.
     * @cfg {String} successProperty Name of the property from which to retrieve the success attribute used by forms.
     * @cfg {String} root name of the property which contains the Array of row objects.
     * @cfg {String} id Name of the property within a row object that contains a record identifier value.
     * @constructor
     * Create a new JsonReader
     * @param {Object} meta Metadata configuration options
     * @param {Object[]/Ext.data.Record constructor} recordType The record definition of the data record to produce.
     */
    Ext.data.JsonReader = function(meta, recordType){
        Ext.data.JsonReader.superclass.constructor.call(this, meta, recordType);
    };
    Ext.extend(Ext.data.JsonReader, Ext.data.DataReader, {
        /**
         * This method is only used by a DataProxy which has retrieved data from a remote server.
         * @param {Object} response The XHR object which contains the JSON data in its responseText.
         * @return {Object} data A data block which is used by an Ext.data.Store object as
         * a cache of Ext.data.Records.
         */
        read : function(response){
            var json = response.responseText;
            var o = eval("("+json+")");
            if(!o) {
                throw {message: "JsonReader.read: Json object not found"};
            }
            return this.readRecords(o);
        },

    	/**
    	 * @ignore
    	 */
        simpleAccess: function(obj, subsc) {
        	return obj[subsc];
        },

    	/**
    	 * @ignore
    	 */
        getJsonAccessor: function(){
            var re = /[\[\.]/;
            return function(expr) {
                try {
                    return(re.test(expr))
                        ? new Function("obj", "return obj." + expr)
                        : function(obj){
                            return obj[expr];
                        };
                } catch(e){}
                return Ext.emptyFn;
            };
        }(),

        /**
         * Create a data block containing Ext.data.Records from an XML document.
         * @param {Object} o An object which contains an Array of row objects in the property specified
         * in the config as 'root, and optionally a property, specified in the config as 'totalProperty'
         * which contains the total size of the dataset.
         * @return {Object} data A data block which is used by an Ext.data.Store object as
         * a cache of Ext.data.Records.
         */
        readRecords : function(o){
            /**
             * After any data loads, the raw JSON data is available for further custom processing.
             * @type Object
             */
            this.jsonData = o;
            var s = this.meta, Record = this.recordType,
                f = Record.prototype.fields, fi = f.items, fl = f.length;

    //      Generate extraction functions for the totalProperty, the root, the id, and for each field
            if (!this.ef) {
                if(s.totalProperty) {
    	            this.getTotal = this.getJsonAccessor(s.totalProperty);
    	        }
    	        if(s.successProperty) {
    	            this.getSuccess = this.getJsonAccessor(s.successProperty);
    	        }
    	        this.getRoot = s.root ? this.getJsonAccessor(s.root) : function(p){return p;};
    	        if (s.id) {
    	        	var g = this.getJsonAccessor(s.id);
    	        	this.getId = function(rec) {
    	        		var r = g(rec);
    		        	return (r === undefined || r === "") ? null : r;
    	        	};
    	        } else {
    	        	this.getId = function(){return null;};
    	        }
                this.ef = [];
                for(var i = 0; i < fl; i++){
                    f = fi[i];
                    var map = (f.mapping !== undefined && f.mapping !== null) ? f.mapping : f.name;
                    this.ef[i] = this.getJsonAccessor(map);
                }
            }

        	var root = this.getRoot(o), c = root.length, totalRecords = c, success = true;
        	if(s.totalProperty){
                var v = parseInt(this.getTotal(o), 10);
                if(!isNaN(v)){
                    totalRecords = v;
                }
            }
            if(s.successProperty){
                var v = this.getSuccess(o);
                if(v === false || v === 'false'){
                    success = false;
                }
            }
            var records = [];
    	    for(var i = 0; i < c; i++){
    		    var n = root[i];
    	        var values = {};
    	        var id = this.getId(n);
    	        for(var j = 0; j < fl; j++){
    	            f = fi[j];
                    var v = this.ef[j](n);
                    values[f.name] = f.convert((v !== undefined) ? v : f.defaultValue);
    	        }
    	        var record = new Record(values, id);
    	        record.json = n;
    	        records[i] = record;
    	    }
    	    return {
    	        success : success,
    	        records : records,
    	        totalRecords : totalRecords
    	    };
        }
    });

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