有没有办法在objective-C中获取SQLite中表的大小？答案

【问题标题】：Is there a way to get the size of a table in SQLite in objective-C?有没有办法在objective-C中获取SQLite中表的大小？
【发布时间】：2015-04-03 17:18:07
【问题描述】：

我觉得没有简单的方法可以做到这一点？获取每个ManagedObject，获取与其链接的所有对象，统计转换后变量的字节数？

【问题讨论】：

你到底要找什么尺寸的？
sqlite.org/lang_aggfunc.html#count
我在这里得到了答案：stackoverflow.com/questions/250940/…。我将查询每个字段后返回的所有值进行汇总。

标签： objective-c sqlite

【解决方案1】：

好的，我找到了获取数据库统计信息所需的解决方案。

按照建议，我直接使用带有 length() 函数的 SQL 查询。然后我可以稍后循环以计算总大小（以字节为单位）。

首先，在您的 XCode 项目中，包含“libsqlite3.0.dylib”

然后，导入库：

#import <sqlite3.h>

最后的实现可能是：

float size;
sqlite3* dbHandle;
NSArray *paths =  NSSearchPathForDirectoriesInDomains(NSDocumentDirectory , NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

NSString* dbFile = [documentsDirectory stringByAppendingPathComponent:@"mybase.sqlite"];

sqlite3_config(SQLITE_CONFIG_SERIALIZED);

int result = sqlite3_open([dbFile UTF8String], &dbHandle);
if (result != SQLITE_OK) {
    NSLog(@"Failure in connecting to the database with result %d",result);
}
else {
    NSLog(@ "Successfully opened connection to DB") ;

    NSString    *query  =   @"SELECT length(HEX(zmyField))/2 FROM zmyTable";
// You have to append 'z' to table and name field due to SQLite naming convention (cf.https://softwareengineering.stackexchange.com/questions/178994/why-do-core-data-sqlite-table-columns-start-with-z)

    const char *sql3 = [[NSString stringWithFormat:query] cStringUsingEncoding:NSUTF8StringEncoding];

    NSMutableArray *results = [NSMutableArray array];

    sqlite3_stmt *sql1Statement;
    int returnCode;
    if(sqlite3_prepare_v2(dbHandle, sql3, -1, &sql1Statement, NULL) != SQLITE_OK)
    {
        NSLog(@"Problem with prepare statement: %s", sqlite3_errmsg(dbHandle));
    }
    else
    {

        while ((returnCode = sqlite3_step(sql1Statement)) == SQLITE_ROW) {
            NSLog(@"SIZE : %f",sqlite3_column_double(sql1Statement, 0));
            size+=sqlite3_column_double(sql1Statement, 0);
        }
        if (returnCode != SQLITE_DONE)
            NSLog(@"Problem with step statement: %s", sqlite3_errmsg(dbHandle));

        sqlite3_finalize(sql1Statement);
    }
}
NSLog(@"TOTAL SIZE for myField in my Table : %f",size);

要获取总 db 大小，或逐个表，甚至逐个字段，您可以使用 SQLite 指令列出所有表和字段名称。然后将 length() 函数应用于循环结果：

表格列表：

SELECT name FROM sqlite_master WHERE type='table'

对于字段：

PRAGMA table_info('myTable')

参考：

http://www.priyaontech.com/2011/09/intro-to-sqlite-for-ios-developers/

How do I find the length (size) of a binary blob in sqlite

https://softwareengineering.stackexchange.com/questions/178994/why-do-core-data-sqlite-table-columns-start-with-z

How to get a list of column names on sqlite3 / iPhone?

【讨论】：