JavaScript: LazyRepo, Instantly cache JSON array REST API response into WebSQL.

LazyRepo.js

/**
 * Copyright 2016 Amri Shodiq
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * 
 *     http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 * 
 */

/**
 * Instantly cache JSON array REST API response into WebSQL.
 */
function LazyRepo(config) {
    var instance = this;
    this.config = config;

    this.getAll = function(datasource, callback, errorcallback) {
        var sql = "SELECT * FROM "+datasource.table;
        query(sql, datasource, callback, errorcallback);
    }
        
    this.findBy = function(field, value, datasource, callback, errorcallback) {
        var sql = "SELECT * FROM "+datasource.table+" WHERE "+field+" = '"+value+"'";
        query(sql, datasource, callback, errorcallback);
    }

    this.findLike = function(field, valuelike, datasource, callback, errorcallback) {
        var sql = "SELECT * FROM "+datasource.table+" WHERE "+field+" LIKE '%"+valuelike+"%'";
        query(sql, datasource, callback, errorcallback);
    }
        
    var select = function(sql, callback, errorcallback) {
        getDatabase().transaction(function(trx) {
            trx.executeSql(
                sql, 
                null, 
                function(trx, results) {
                    callback(results);
                }, 
                function(trx, error) {
                    callback(null);
                    errorcallback(error);
                }
            );
        });
    }
            
    var db = null;
    var getDatabase = function() {
        if (db == null) {
            db = openDatabase(
                instance.config.name, 
                instance.config.version, 
                instance.config.realname, 
                instance.config.size
            );
        }
        return db;
    }

    var query = function(sql, datasource, callback, errorcallback) {
        isDataExists(datasource, function(yes) {
            if (yes) {
                select(sql, callback, errorcallback);
            } else {
                $.ajax({
                    url: datasource.uri,
                    dataType: 'json',
                    success: function( result ) {
                        saveDatas(result, datasource.table, function() {
                            select(sql, callback);        
                        });
                    }
                });
            }
        });
    }
    
    var saveDatas = function(result, table, onFinished) {
        getDatabase().transaction(function(trx) {
            result.forEach(function(element, index) {
                var sql = createInsertQuery(element, table);
                trx.executeSql(
                    sql, 
                    createInsertValues(element), 
                    function(transaction, sqlResultSet) {
                        console.log("Succeed");
                    },
                    function(transaction, error) {
                        console.log("SQL: "+sql);
                        console.log("Error: "+error.message);
                    }
                );
            });
            onFinished();
        });
    }
    
    var createInsertValues = function(object) {
        var result = [];
        var properties = Object.keys(object);
        for (var i=0; i<properties.length; i++) {
            result.push(object[properties[i]]);
        }
        return result;
    }

    var createInsertQuery = function(object, table) {
        var sql = "INSERT INTO "+table+" VALUES (";
        var properties = Object.keys(object);
        for (var i=0; i<properties.length; i++) {
            if (i==0) {
                sql += "?";
            } else {
                sql += ", ?";
            }
        }
        sql += ")";

        return sql;
    }

    var isDataExists = function(datasource, callback) {
        getDatabase().transaction(function(trx) {
            createTableIfNotExists(
                datasource, 
                trx, 
                function() {
                    var sql = "SELECT * FROM "+datasource.table;
                    trx.executeSql(sql, null, function(trx, results) {
                        if (results.rows.length > 0) {
                            callback(true);
                        } else {
                            callback(false);
                        }
                    }); 
                }, 
                function() {
                    callback(false);
                }
            );
        });
    }
    
    var createTableIfNotExists = function(datasource, trx, onSucceed, onError) {
        var sql = "CREATE TABLE IF NOT EXISTS "+datasource.table+" (";
        var len = datasource.fields.length;
        for (var i=0; i<len; i++) {
            if (i==0) {
                sql += datasource.fields[i];
            } else {
                sql += ", "+datasource.fields[i];
            }
        }
        sql += ")";

        trx.executeSql(
            sql,
            null,
            function(transaction, sqlResultSet) {
                onSucceed();
            },
            function(transaction, error) {
                onError();
            }
        );
    }

};