DML

在本章中，我们将讨论如何在Salesforce中执行不同的数据库修改功能。 有两个说我们可以执行功能。

DML声明

DML是为执行插入，更新，删除，复制，恢复记录，合并记录或转换引导操作而执行的操作。

DML是Apex中最重要的部分之一，因为几乎每个业务案例都涉及对数据库的更改和修改。

数据库方法

您可以使用DML语句执行的所有操作也可以使用数据库方法执行。 数据库方法是可用于执行DML操作的系统方法。 与DML语句相比，数据库方法提供了更大的灵活性。

在本章中，我们将讨论使用DML语句的第一种方法。 我们将在后续章节中查看数据库方法。

DML声明

现在让我们再次考虑化学品供应商公司的实例。 我们的发票记录包含状态，已付金额，剩余金额，下一个付款日期和发票编号等字段。 今天创建并且状态为“待定”的发票应更新为“付费”。

插入操作 (Insert Operation)

插入操作用于在数据库中创建新记录。 您可以使用Insert DML语句创建任何标准或自定义对象的记录。

Example

我们可以在APEX_Invoice__c对象中创建新记录，因为每天都会为新客户订单生成新发票。 我们将首先创建一个客户记录，然后我们可以为该新客户记录创建一个发票记录。

// fetch the invoices created today, Note, you must have at least one invoice 
// created today
List<apex_invoice__c> invoiceList = [SELECT id, Name, APEX_Status__c,
   createdDate FROM APEX_Invoice__c WHERE createdDate = today];
// create List to hold the updated invoice records
List<apex_invoice__c> updatedInvoiceList = new List<apex_invoice__c>();
APEX_Customer__c objCust = new APEX_Customer__C();
objCust.Name = 'Test ABC';
//DML for Inserting the new Customer Records
insert objCust;
for (APEX_Invoice__c objInvoice: invoiceList) {
   if (objInvoice.APEX_Status__c == 'Pending') {
      objInvoice.APEX_Status__c = 'Paid';
      updatedInvoiceList.add(objInvoice);
   }
}
// DML Statement to update the invoice status
update updatedInvoiceList;
// Prints the value of updated invoices
System.debug('List has been updated and updated values are' + updatedInvoiceList);
// Inserting the New Records using insert DML statement
APEX_Invoice__c objNewInvoice = new APEX_Invoice__c();
objNewInvoice.APEX_Status__c = 'Pending';
objNewInvoice.APEX_Amount_Paid__c = 1000;
objNewInvoice.APEX_Customer__c = objCust.id;
// DML which is creating the new Invoice record which will be linked with newly
// created Customer record
insert objNewInvoice;
System.debug('New Invoice Id is '+objNewInvoice.id+' and the Invoice Number is'
   + objNewInvoice.Name);

更新操作 (Update Operation)

更新操作是对现有记录执行更新。 在此示例中，我们将现有Invoice记录的Status字段更新为'Paid'。

Example

// Update Statement Example for updating the invoice status. You have to create
and Invoice records before executing this code. This program is updating the
record which is at index 0th position of the List.
// First, fetch the invoice created today
List<apex_invoice__c> invoiceList = [SELECT id, Name, APEX_Status__c,
createdDate FROM APEX_Invoice__c];
List<apex_invoice__c> updatedInvoiceList = new List<apex_invoice__c>();
// Update the first record in the List
invoiceList[0].APEX_Status__c = 'Pending';
updatedInvoiceList.add(invoiceList[0]);
// DML Statement to update the invoice status
update updatedInvoiceList;
// Prints the value of updated invoices
System.debug('List has been updated and updated values of records are' 
   + updatedInvoiceList[0]);

Upsert操作

Upsert Operation用于执行更新操作，如果数据库中不存在要更新的记录，则还要创建新记录。

Example

假设客户对象中的客户记录需要更新。 我们将更新现有客户记录（如果已存在），否则创建新记录。 这将基于字段APEX_External_Id__c的值。 该字段将是我们的字段，用于识别记录是否已存在。

Note - 在执行此代码之前，请在Customer对象中创建一条记录，并将外部Id字段值设置为“12341”，然后执行下面给出的代码 -

// Example for upserting the Customer records
List<apex_customer__c> CustomerList = new List<apex_customer__c>();
for (Integer i = 0; i < 10; i++) {
   apex_customer__c objcust=new apex_customer__c(name = 'Test' +i,
   apex_external_id__c='1234' +i);
   customerlist.add(objcust);
} //Upserting the Customer Records
upsert CustomerList;
System.debug('Code iterated for 10 times and created 9 records as one record with 
   External Id 12341 is already present');
for (APEX_Customer_c objCustomer: CustomerList) {
   if (objCustomer.APEX_External_Id_c == '12341') {
      system.debug('The Record which is already present is '+objCustomer);
   }
}

删除操作 (Delete Operation)

您可以使用Delete DML执行删除操作。

Example

在这种情况下，我们将删除为测试目的而创建的发票，即包含名称为“Test”的发票。

您也可以从Developer控制台执行此代码段，而无需创建类。

// fetch the invoice created today
List<apex_invoice__c> invoiceList = [SELECT id, Name, APEX_Status__c,
createdDate FROM APEX_Invoice__c WHERE createdDate = today];
List<apex_invoice__c> updatedInvoiceList = new List<apex_invoice__c>();
APEX_Customer__c objCust = new APEX_Customer__C();
objCust.Name = 'Test';
// Inserting the Customer Records
insert objCust;
for (APEX_Invoice__c objInvoice: invoiceList) {
   if (objInvoice.APEX_Status__c == 'Pending') {
      objInvoice.APEX_Status__c = 'Paid';
      updatedInvoiceList.add(objInvoice);
   }
}
// DML Statement to update the invoice status
update updatedInvoiceList;
// Prints the value of updated invoices
System.debug('List has been updated and updated values are' + updatedInvoiceList);
// Inserting the New Records using insert DML statement
APEX_Invoice__c objNewInvoice = new APEX_Invoice__c();
objNewInvoice.APEX_Status__c = 'Pending';
objNewInvoice.APEX_Amount_Paid__c = 1000;
objNewInvoice.APEX_Customer__c = objCust.id;
// DML which is creating the new record
insert objNewInvoice;
System.debug('New Invoice Id is' + objNewInvoice.id);
// Deleting the Test invoices from Database
// fetch the invoices which are created for Testing, Select name which Customer Name
// is Test.
List<apex_invoice__c> invoiceListToDelete = [SELECT id FROM APEX_Invoice__c
   WHERE APEX_Customer__r.Name = 'Test'];
// DML Statement to delete the Invoices
delete invoiceListToDelete;
System.debug('Success, '+invoiceListToDelete.size()+' Records has been deleted');

取消删除操作

您可以取消删除已删除且存在于回收站中的记录。 删除的记录所具有的所有关系也将被恢复。

Example

假设，需要恢复上一个示例中删除的记录。 这可以使用以下示例来实现。 此示例中的代码已针对此示例进行了修改。

// fetch the invoice created today
List<apex_invoice__c> invoiceList = [SELECT id, Name, APEX_Status__c,
createdDate FROM APEX_Invoice__c WHERE createdDate = today];
List<apex_invoice__c> updatedInvoiceList = new List<apex_invoice__c>();
APEX_Customer__c objCust = new APEX_Customer__C();
objCust.Name = 'Test';
// Inserting the Customer Records
insert objCust;
for (APEX_Invoice__c objInvoice: invoiceList) {
   if (objInvoice.APEX_Status__c == 'Pending') {
      objInvoice.APEX_Status__c = 'Paid';
      updatedInvoiceList.add(objInvoice);
   }
}
// DML Statement to update the invoice status
update updatedInvoiceList;
// Prints the value of updated invoices
System.debug('List has been updated and updated values are' + updatedInvoiceList);
// Inserting the New Records using insert DML statement
APEX_Invoice__c objNewInvoice = new APEX_Invoice__c();
objNewInvoice.APEX_Status__c = 'Pending';
objNewInvoice.APEX_Amount_Paid__c = 1000;
objNewInvoice.APEX_Customer__c = objCust.id;
// DML which is creating the new record
insert objNewInvoice;
System.debug('New Invoice Id is '+objNewInvoice.id);
// Deleting the Test invoices from Database
// fetch the invoices which are created for Testing, Select name which Customer Name
// is Test.
List<apex_invoice__c> invoiceListToDelete = [SELECT id FROM APEX_Invoice__c
   WHERE APEX_Customer__r.Name = 'Test'];
// DML Statement to delete the Invoices
delete invoiceListToDelete;
system.debug('Deleted Record Count is ' + invoiceListToDelete.size());
System.debug('Success, '+invoiceListToDelete.size() + 'Records has been deleted');
// Restore the deleted records using undelete statement
undelete invoiceListToDelete;
System.debug('Undeleted Record count is '+invoiceListToDelete.size()+'. This should 
   be same as Deleted Record count');