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Reading records from your database typically involves using one of the 3 finder methods available in Wheels: findByKey(), findOne(), and findAll(). The first 2 of these, (findByKey() and findOne()), return an object to you, while the last one (findAll()) returns the result from a cfquery tag. Fetching a Row by Primary Key ValueLet's start by looking at the simplest of the finder methods, findByKey(). This method takes one argument: the primary key (or several keys if you're using composite keys) of the record you want to get. If the record exists, it is returned to you as an object. If not, Wheels will return the boolean value false. In the following example, we assume that the params.key variable has been created from the URL (for example an URL such as http://localhost/blog/viewauthor/7) In your controller: <cfset author = model("author").findByKey(params.key)>
<cfif NOT IsObject(author)>
<cfset flashInsert(message="Author #params.key# was not found")>
<cfset redirectTo(back=true)>
</cfif>In your view: <cfoutput>Hello, #author.firstName# #author.lastName#!</cfoutput> Fetching a Row by a Value Other Than the Primary KeyOften, you'll find yourself wanting to get a record (or many) based on a criteria other than just the primary key value though. As an example, let's say that you want to get the last order made by a customer. You can achieve this by using the findOne() method like so: <cfset anOrder = model("order").findOne(order="datePurchased DESC")>In this case, findOne() will force the maxRows argument of the cfquery tag to 1. Because you're specifically asking to get one record from the database, Wheels will return this as an object. Fetching Multiple RowsYou can use findAll() when you are asking to get one or more records from the database. Wheels will return this as a cfquery result (which could be empty if nothing was found based on your criteria). Arguments for findOne() and findAll()Besides the difference in the default return type, findOne() and findAll() accept the same arguments. Let's have a closer look at these arguments. select ArgumentThis maps to the SELECT clause of the SQL statement. Wheels is pretty smart when it comes to figuring out what to select from the database table(s). For example, if nothing is passed in to the select argument, Wheels will assume that you want all columns returned and create a SELECT clause looking something like this: artists.id,artists.name As you can see, Wheels knows that the artist model is mapped to the artists table and will prepend the table name to the column names accordingly. If you have mapped columns to a different property name in your application, Wheels will take this into account as well. The end result then could look like this: artists.id,artists.fname AS firstName If you select from more than one table (see the include argument below) and there are ambiguous column names, Wheels will sort this out for you by prepending the model name to the column name. Let's say you have a column called name in both the artists and albums tables. The SELECT clause will be created like this: artists.name,albums.name AS albumName If you use the include argument a lot, you will love this feature as it saves a lot of typing. If you don't want to return all properties, you can override this behavior by passing in a list of the properties you want returned. If you want to take full control over the SELECT clause, you can do so by specifying the table names (i.e. author.firstName) in the select argument or by using alias names (i.e. firstname AS firstName). If Wheels comes across the use of any of these techniques, it will assume you know what you're doing and pass on the select argument straight to the SELECT clause with no changes. A tip is to turn on debugging when you're learning Wheels so you can get a good understanding of how Wheels creates the SQL statements. where ArgumentThis maps to the WHERE clause of the SQL statement. Wheels will also convert all your input to cfqueryparam tags for you automatically. There are some limitations to what you can use in the where argument, but the following SQL will work: =, <>, <, <=, >, >=, LIKE, AND, and OR. (Note that it's a requirement to write SQL keywords in upper case.) In addition to this, you can use parentheses to group conditional SQL statements together. order ArgumentThis maps to the ORDER clause of the SQL statement. If you don't specify an order at all, none will be used (makes sense, eh?). So in those cases, the database engine will decide in what order to return the records. There is one exception to this. If you paginate the records (by passing in the page argument) without specifying the order, Wheels will order the results by the primary key column. This is because pagination relies on having unique records to order by. include ArgumentThis is a powerful feature that you can use if you have set up associations in your models. If, for example, you have specified that one author has many articles, then you can return all authors and articles in the same call by doing this: <cfset bobsArticles = model("author").findAll(where="firstName='Bob'", include="articles")>maxRows ArgumentThis limits the number of records to return. Please note that if you call findAll() with maxRows=1, you will still get a cfquery result back and not an object. (We recommend using findOne() in this case if you want for an object to be returned.) page and perPage ArgumentsSet these if you want to get paginated data back. So if you wanted records 11-20, for example, you write this code: <cfset bobsArticles = model("author").findAll(where="firstName='Bob'", include="articles", page=2, perPage=10)>cache ArgumentThis is the number of minutes to cache the query for. This is eventually passed on to the cachedwithin attribute of the cfquery tag. returnAs ArgumentIn the beginning of this chapter, we said that you either get a query or an object back depending on the method that you call. But you can actually specify the return type so that you get either an object, a query, or an array of objects back. To do this, you use the returnAs argument. If you want an array of objects back from a findAll() call, for example, you can do this: <cfset users = model("user").findAll(returnAs="objects")>On findOne() and findByKey(), you can set this argument to either object or query. On the findAll() method, you can set it to objects (note the plural) or query. We recommend sticking to this convention as much as possible because of the CFML engines' slow CreateObject() function. Be careful when setting returnAs to objects. You won't want to create a lot of objects in your array and slow down your application unless you absolutely need to.
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I would like more examples on the use of include in findAll(), and in particular, what is the entire requirements (what do we need in the controller, model and so forth to get this association working. Email me at doronkatz@mac.com Cheers