Condition Micro Language

Condition micro-language

Both the Python and Javascript bindings for MapR DB support a micro language for conditions. These conditions are JSON object and have several forms of short-cuts to handle the most common cases. In general, a condition looks like a mirror of some of the fields in the document except that values are replaced by comparison functions. The most common short-cut is that scalar values are short-cuts for an equality test with those values.

For example, equality with a scalar value can have a short-cut expression:

{ "country" : "China" } // country == "China"

But testing for equality with structures is not allowed:

{ "country" : ["China", "United States"] }

{ "country" : {"bag": "China"} }

Instead, do this:

{ "country" : {"$eq": ["China","United States"]} } 

Many other tests are also available.

{ "age" : { "$gt" : 34 } } // age > 34
{ "age" : { "$gte" : 34 } } // age >= 34
{ "age" : { "$lt" : 34 } } // age < 34
{ "age" : { "$lte" : 34 } } // age <= 34
{ "age" : { "$neq" : 34 } } // age != 34
{ "age" : { "$between" : [30,40] } } // BETWEEN 30 and 40 (inclusive)
{ "age" : { "$in" : [20,25,30] } } // IN [20, 25, 30]
{ "age" : { "$exists" : true} }
{ "age" : { "$exists" : false} }

The complete list of available operators is shown in the following table, but you should note that there is no implicit conversion of types done. Note also that comparison with null is done as in Java, not as in SQL. This means that null == null.

Operator	Meaning
$eq, $equal, =	Is equal to.
$ne, $neq, !=	Not equal to.
$lt, $less, <	Less than. Should work for either strings or numbers, but comparing strings to numbers is not defined.
$lte, $le, <=	Less than or equal.
$gt, $greater, >	Greater than.
$ge, $gte, >=	Greater than or equal
$between	The value of the field should be a list of two values. The expression {"x": {"$between":[u,v]}} is equivalent to {"x": {"$and":[{$ge:u}, {$le:v}]} }.
$in	The value of the field is in a literal list. {x: {$in: [1,2,34]}} is true if x is any of 1, 2 or 34.
!$in	Not in.
$exists	The field exists or not according to the the value supplied. Note that missing is different from null.
$like, $matches	The value of the field matches a regular expression.
!$like, !$matches	The value of the field does not match a regular expression.
$and, $or	Combining forms that combine multiple conditions. The argument is a list of condition expressions.

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If you want to set a condition on multiple fields, simply include all of the tests in a single object

{ "country" : "China", "age" : 34 } // country = "China" AND age = 34

Note that if you need multiple conditions on a single field, you can use the $and and $or combining forms:

{ "country" : {"$or":{"China", "US"}, "age": {"$and":[{"$ge":30}, {"$lt":40}] } } 

In contrast, if you want any of several conditions to be satisfied, simply put all the alternatives in a list.

[ condition1, condition2, ... ] // condition1 OR condition2

Extension of this mechanism to other tests is an area of active discussion.

Mutation

The mutation object is sent to the server and all operations are used on the server side.

{"field" : { "$set" : "value"}  }
{"age" : { "$set" : 34}  }  // set age to 34
{"age" : { "$set" : 34} , "country" : { "$set": "USA"}  }  // set age to 34 and country to USA
{ "interests" : { "$set" : ["x", "y"] } } // set interests to an array
{ "address" : { "$set" : { "t" : "home"} } } // set address to an Object

{"field" : { "$setOrReplace" : "value"}  }
{"age" : { "$setOrReplace" : 34}  }  // set age to 34
{"age" : { "$setOrReplace" : 34, "country" : { "$setOrReplace" : "USA"}  }  // set age to 34 and country to USA

{ "field" : { "$append" : "value" }}
{ "name" :  { "$append" : "Doe" }} //  append Doe to the string if string or array if array eg: "John" = "JoeDoe" OR ["John"] = ["John" , "Doe"]

{"field" : { "$setOrReplace" : "value"}  }
{"age" : { "$setOrReplace" : 34}  }  // set age to 34
{"age" : { "$setOrReplace" : 34, "country" : { "$setOrReplace" : "USA"}  }  // set age to 34 and country to USA

{"field" : { "$inc" : value } }
{"age" : { "$inc" : 1 } } //  increment one value by a specified amount