cocoa用nspredicate描述查詢的方式，原理類似於在資料庫中進行查詢
計算謂詞：
//基本的查詢
nspredicate *predicate;
predicate = [nspredicate predicatewithformat: @"name == 'herbie'"
];
bool
match = [predicate evaluatewithobject: car];
nslog (@"%s"
, (match) ?
"yes"
: "no"
);
//在整個cars裡面迴圈比較
predicate = [nspredicate predicatewithformat: @"engine.horsepower > 150"
];
nsarray *cars = [garage cars];
for(car *car in [garage cars])
} //輸出完整的資訊
predicate = [nspredicate predicatewithformat: @"engine.horsepower > 150"
];
nsarray *results;
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
//含有變數的謂詞
nspredicate *predicatetemplate = [nspredicate predicatewithformat:@"name == $name"
];
nsdictionary *vardict;
vardict = [nsdictionary dictionarywithobjectsandkeys:
@"herbie"
, @"name"
, nil];
predicate = [predicatetemplate predicatewithsubstitutionvariables: vardict];
nslog(@"snorgle: %@"
, predicate);
match = [predicate evaluatewithobject: car];
nslog (@"%s"
, (match) ?
"yes"
: "no"
);
//注意不能使用$variable作為路徑名，因為它值代表值
//謂詞字元竄還支援c語言中一些常用的運算子
predicate = [nspredicate predicatewithformat:
@"(engine.horsepower > 50) and (engine.horsepower < 200)"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"oop %@"
, results);
predicate = [nspredicate predicatewithformat: @"name < 'newton'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, [results valueforkey: @
"name"
]);
//強大的陣列運算子
predicate = [nspredicate predicatewithformat:
@"engine.horsepower between "
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
nsarray *betweens = [nsarray arraywithobjects:
[nsnumber numberwithint: 50], [nsnumber numberwithint: 200], nil];
predicate = [nspredicate predicatewithformat: @"engine.horsepower between %@"
, betweens];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
predicatetemplate = [nspredicate predicatewithformat: @"engine.horsepower between $powers"
];
vardict = [nsdictionary dictionarywithobjectsandkeys: betweens, @"powers"
, nil];
predicate = [predicatetemplate predicatewithsubstitutionvariables: vardict];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
//in運算子
predicate = [nspredicate predicatewithformat: @"name in "
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, [results valueforkey: @
"name"
]);
predicate = [nspredicate predicatewithformat: @"self.name in "
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, [results valueforkey: @
"name"
]);
names = [cars valueforkey: @"name"
];
predicate = [nspredicate predicatewithformat: @"self in "
];
results = [names filteredarrayusingpredicate: predicate];//這裡限制了self的範圍
nslog (@"%@"
, results);
//beginswith,endswith,contains
//附加符號，[c],[d],[cd],c表示不區分大小寫，d表示不區分發音字元，cd表示什麼都不區分
predicate = [nspredicate predicatewithformat: @"name beginswith 'bad'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
predicate = [nspredicate predicatewithformat: @"name beginswith 'herb'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
predicate = [nspredicate predicatewithformat: @"name beginswith[cd] 'herb'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
//like運算子（萬用字元）
predicate = [nspredicate predicatewithformat: @"name like[cd] '*er*'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
predicate = [nspredicate predicatewithformat: @"name like[cd] '???er*'"
];
results = [cars filteredarrayusingpredicate: predicate];
nslog (@"%@"
, results);
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