1.如果想创建一个带有coredata的程序,要在项目初始化的时候勾选中
2.创建完成之后,会发现在appdelegate里多出了几个属性,和2个方法
复制代码 代码如下:
<span style="font-size:18px;">
@property (readonly, strong, nonatomic) nsmanagedobjectcontext *managedobjectcontext;
@property (readonly, strong, nonatomic) nsmanagedobjectmodel *managedobjectmodel;
@property (readonly, strong, nonatomic) nspersistentstorecoordinator *persistentstorecoordinator;
- (void)savecontext;
- (nsurl *)applicationdocumentsdirectory;</span>
core data数据持久化是对sqlite的一个升级，它是ios集成的，在说core data之前，我们先说说在coredata中使用的几个类。
（1）nsmanagedobjectmodel(被管理的对象模型)
相当于实体，不过它包含 了实体间的关系
(2)nsmanagedobjectcontext(被管理的对象上下文)
操作实际内容
作用：插入数据 查询 更新 删除
（3）nspersistentstorecoordinator(持久化存储助理)
相当于数据库的连接器
(4)nsfetchrequest(获取数据的请求)
相当于查询语句
(5)nspredicate(相当于查询条件)
(6)nsentitydescription(实体结构)
(7)后缀名为.xcdatamodel的包
里面的.xcdatamodel文件，用数据模型编辑器编辑
编译后为.momd或.mom文件，这就是为什么文件中没有这个东西，而我们的程序中用到这个东西而不会报错的原因。
3.如果想创建一个实体对象的话,需要点击.xcdatamodel,add entity,添加想要的字段
4.生成对象文件,command+n,然后选中coredata里的nsmanagerobjectsubclass进行关联,选中实体创建
5.添加数据
复制代码 代码如下:
person *newperson = [nsentitydescription insertnewobjectforentityforname:@"person" inmanagedobjectcontext:self.managedobjectcontext];
if (newperson == nil){
nslog(@"failed to create the new person.");
return no;
}
newperson.firstname = paramfirstname;
newperson.lastname = paramlastname;
newperson.age = [nsnumber numberwithunsignedinteger:paramage];
nserror *savingerror = nil;
if ([self.managedobjectcontext save:&savingerror]){
return yes;
} else {
nslog(@"failed to save the new person. error = %@", savingerror);
}
nsentitydescription（实体结构）相当于表格结构
6.取出数据查询
复制代码 代码如下:
/* create the fetch request first */
nsfetchrequest *fetchrequest = [[nsfetchrequest alloc] init];
/* here is the entity whose contents we want to read */
nsentitydescription *entity =
[nsentitydescription
entityforname:@"person"
inmanagedobjectcontext:self.managedobjectcontext];
/* tell the request that we want to read the
contents of the person entity */
[fetchrequest setentity:entity];
nserror *requesterror = nil;
/* and execute the fetch request on the context */
nsarray *persons =
[self.managedobjectcontext executefetchrequest:fetchrequest
error:&requesterror];
/* make sure we get the array */
if ([persons count] > 0){
/* go through the persons array one by one */
nsuinteger counter = 1;
for (person *thisperson in persons){
nslog(@"person %lu first name = %@",
(unsigned long)counter,
thisperson.firstname);
nslog(@"person %lu last name = %@",
(unsigned long)counter,
thisperson.lastname);
nslog(@"person %lu age = %ld",
(unsigned long)counter,
(unsigned long)[thisperson.age unsignedintegervalue]);
counter++;
}
} else {
nslog(@"could not find any person entities in the context.");
}
7.删除数据
复制代码 代码如下:
/* create the fetch request first */
nsfetchrequest *fetchrequest = [[nsfetchrequest alloc] init];
/* here is the entity whose contents we want to read */
nsentitydescription *entity =
[nsentitydescription
entityforname:@"person"
inmanagedobjectcontext:self.managedobjectcontext];
/* tell the request that we want to read the
contents of the person entity */
[fetchrequest setentity:entity];
nserror *requesterror = nil;
/* and execute the fetch request on the context */
nsarray *persons =
[self.managedobjectcontext executefetchrequest:fetchrequest
error:&requesterror];
if ([persons count] > 0){
/* delete the last person in the array */
person *lastperson = [persons lastobject];
[self.managedobjectcontext deleteobject:lastperson];
nserror *savingerror = nil;
if ([self.managedobjectcontext save:&savingerror]){
nslog(@"successfully deleted the last person in the array.");
} else {
nslog(@"failed to delete the last person in the array.");
}
} else {
nslog(@"could not find any person entities in the context.");
}
8.排序
复制代码 代码如下:
<pre code_snippet_id="243955" snippet_file_name="blog_20140319_5_4289257" name="code" class="objc">nssortdescriptor *agesort =
[[nssortdescriptor alloc] initwithkey:@"age"
ascending:yes];
nssortdescriptor *firstnamesort =
[[nssortdescriptor alloc] initwithkey:@"firstname"
ascending:yes];
nsarray *sortdescriptors = [[nsarray alloc] initwithobjects:
agesort,
firstnamesort, nil nil];
fetchrequest.sortdescriptors = sortdescriptors; </pre><p></p>
<pre></pre>
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<span style="background-color:rgb(255,255,255)">注意</span><span style="font-size:18px; background-color:rgb(255,255,255)">ascending:yes 属性决定排序顺序</span><span style="background-color:rgb(255,255,255)"><span style="font-size:18px"><br>
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