Re: SQL?
Re: SQL?
- Subject: Re: SQL?
- From: "Jerry W. Walker" <email@hidden>
- Date: Wed, 8 Feb 2006 23:15:55 -0500
Hi, Jim,
All of the advice you've been given is correct, but focus on the
EOQualifier (which is used in the EOFetchSpecification). In
particular, study the static EOQualifier method:
qualifierWithQualifierFormat(String format, NSArray arguments);
You set up an EOQualifier based on the properties in your Entity
rather than the columns of your table. This carries two advantages:
* it allows you to focus on the object model rather than
bifurcating your view between object model and database tables
* it provides the ability to set up qualifiers based not only on
column values, but on values extracted through relations.
Finally, the qualifier can be used both to filter the data returned
from a fetch as well as to further filter data from an NSArray
already holding the results of an earlier fetch.
In case you need to do such a fetch, here is the set of classes
usually needed in a typical context in which they would be used.
Having their names, as well as the names of the methods typically
used should allow you to look them up conveniently in the API
documentation:
The general hierarchy of classes needed for a fetch is:
EOEditingContext ec = defaultEditingContext();
EOQualifier qual = EOQualifier.qualifierWithQualifierFormat
("someAttribute > %@ AND someOtherAttribute = %@", arrayOfTwoValues);
EOSortOrdering so1 = new EOSortOrdering("someAttribute",
EOSortOrdering.CompareCaseInsensitiveAscending);
EOSortOrdering so2 = new EOSortOrdering("someOtherAttribute",
EOSortOrdering.CompareDescending);
NSArray sortOrdering = new NSArray(new Object[] {so1, so2});
EOFetchSpecification mySpec = new EOFetchSpecification
("EntityName", qual, sortOrdering);
NSArray myResults = ec.objectsWithFetchSpecification(mySpec);
The above represents the general case. You can shortcut some of that
for simpler cases using the EOUtilities.objectsForEntityNamed()
method and others like it (e.g. objectsMatchingKeyAndValue(),
objectsMatchingValues(), etc.).
If you have already fetched data into an array and wish to further
filter the data in that array, you can still use the EOQualifier as
follows:
NSArray myFilteredResults =
EOQualifier.filteredArrayWithQualifier(myResults,
myAdditionalQualifier);
The above statement would apply the qualifier to the array just as it
would have applied it to a fetch, creating a new array with the
filtered results which you were looking for. Finally, if your initial
results are in an NSMutableArray and you would like to modify that
array by further filtering, you would use the EOQualifier method
filterArrayWithQualifier. Notice the subtle difference in the method
name from that earlier.
If you found this helpful and would like more information on "the
WebObjects Way of fetching data" please see the message I sent to
someone on this topic last year:
http://www.wodeveloper.com/omniLists/webobjects-dev/2005/July/
msg00118.html
The level of discourse is probably a bit below your level, but you
might still find it helpful.
Regards,
Jerry
On Feb 8, 2006, at 7:45 PM, Sacha Michel Mallais wrote:
On Feb 8, 2006, at 4:33 PM, Jim Wong wrote:
Can I use SQL statements in WO to extract certain rows in my
entity? Basically I want to filter my entity object for certain
rows of data. how to do this?
Yes you can, but you generally don't want to. Take a look at the
documentation for EOFetchSpecification.
http://developer.apple.com/documentation/WebObjects/Reference/API/
com/webobjects/eocontrol/EOFetchSpecification.html
If you _must_ use SQL (usually only necessary for optimization),
then you'll have to do something like this:
...
--
__ Jerry W. Walker,
WebObjects Developer/Instructor for High Performance Industrial
Strength Internet Enabled Systems
email@hidden
203 278-4085 office
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| References: | |
| | >SQL? (From: Jim Wong <email@hidden>) |
| | >Re: SQL? (From: Sacha Michel Mallais <email@hidden>) |