20.4.3.3 Find Documents

To return all documents in a collection, use the find() method without specifying search conditions. For example, the following operation returns all documents in the countryinfo collection.

mysql-py> db.countryinfo.find()
[
     {
          "GNP": 828,
          "IndepYear": null,
          "Name": "Aruba",
          "_id": "ABW",
          "demographics": {
              "LifeExpectancy": 78.4000015258789,
              "Population": 103000
          },
          "geography": {
              "Continent": "North America",
              "Region": "Caribbean",
              "SurfaceArea": 193
          },
          "government": {
              "GovernmentForm": "Nonmetropolitan Territory of The Netherlands",
              "HeadOfState": "Beatrix"
          }
          ...
      }
 ]
240 documents in set (0.00 sec)

The method produces results that contain operational information in addition to all documents in the collection.

An empty set (no matching documents) returns the following information:

Empty set (0.00 sec) 

You can include search conditions with the find() method. The syntax for expressions that form a search condition is the same as that of traditional MySQL Chapter 12, Functions and Operators. You must enclose all expressions in quotes. For the sake of brevity, some of the examples do not display output.

A simple search condition could consist of the Name field and a value we know is in a document. The following example returns a single document:

mysql-py> db.countryinfo.find("Name = 'Australia'")
[
    {
        "GNP": 351182,
        "IndepYear": 1901,
        "Name": "Australia",
        "_id": "AUS",
        "demographics": {
            "LifeExpectancy": 79.80000305175781,
            "Population": 18886000
        },
        "geography": {
            "Continent": "Oceania",
            "Region": "Australia and New Zealand",
            "SurfaceArea": 7741220
        },
        "government": {
            "GovernmentForm": "Constitutional Monarchy, Federation",
            "HeadOfState": "Elisabeth II"
        }
    }
]

The following example searches for all countries that have a GNP higher than $500 billion. The countryinfo collection measures GNP in units of million.

mysql-py> db.countryinfo.find("GNP > 500000")
...[output removed]
10 documents in set (0.00 sec)

The Population field in the following query is embedded within the demographics object. To access the embedded field, use a period between demographics and Population to identify the relationship. Document and field names are case-sensitive.

mysql-py> db.countryinfo.find("GNP > 500000 and demographics.Population < 100000000")
...[output removed]
6 documents in set (0.00 sec)

Arithmetic operators in the following expression are used to query for countries with a GNP per capita higher than $30000. Search conditions can include arithmetic operators and most MySQL functions.

mysql-py> db.countryinfo.find("GNP*1000000/demographics.Population > 30000")
...[output removed]
9 documents in set, 7 warnings (0.00 sec)
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0
Warning (Code 1365): Division by 0

You can separate a value from the search condition by using the bind() method. For example, instead of specifying a hard-coded country name as the condition, substitute a named placeholder consisting of a colon followed by a name that begins with a letter, such as country. Then use the bind(placeholder, value) method as follows:

mysql-py> db.countryinfo.find("Name = :country").bind("country", "Italy")
[
    {
        "GNP": 1161755,
        "IndepYear": 1861,
        "Name": "Italy",
        "_id": "ITA",
        "demographics": {
            "LifeExpectancy": 79,
            "Population": 57680000
        },
        "geography": {
            "Continent": "Europe",
            "Region": "Southern Europe",
            "SurfaceArea": 301316
        },
        "government": {
            "GovernmentForm": "Republic",
            "HeadOfState": "Carlo Azeglio Ciampi"
        }
    }
]
1 document in set (0.01 sec)

You can use placeholders and the bind() method to create saved searches which you can then call with different values. For example to create a saved search for a country:

mysql-py> myFind = db.countryinfo.find("Name = :country")
mysql-py> myFind.bind('country', 'France')
[
    {
        "GNP": 1424285,
        "IndepYear": 843,
        "Name": "France",
        "_id": "FRA",
        "demographics": {
            "LifeExpectancy": 78.80000305175781,
            "Population": 59225700
        },
        "geography": {
            "Continent": "Europe",
            "Region": "Western Europe",
            "SurfaceArea": 551500
        },
        "government": {
            "GovernmentForm": "Republic",
            "HeadOfState": "Jacques Chirac"
        }
    }
]
1 document in set (0.0028 sec)

mysql-py> myFind.bind('country', 'Germany')
[
    {
        "GNP": 2133367, 
        "IndepYear": 1955, 
        "Name": "Germany", 
        "_id": "DEU", 
        "demographics": {
            "LifeExpectancy": 77.4000015258789, 
            "Population": 82164700
        }, 
        "geography": {
            "Continent": "Europe", 
            "Region": "Western Europe", 
            "SurfaceArea": 357022
        }, 
        "government": {
            "GovernmentForm": "Federal Republic", 
            "HeadOfState": "Johannes Rau"
        }
    }
]
1 document in set (0.0026 sec)

You can return specific fields of a document, instead of returning all the fields. The following example returns the GNP and Name fields of all documents in the countryinfo collection matching the search conditions.

Use the fields() method to pass the list of fields to return.

mysql-py> db.countryinfo.find("GNP > 5000000").fields(["GNP", "Name"])
[
    {
        "GNP": 8510700,
        "Name": "United States"
    }
]
1 document in set (0.00 sec)

In addition, you can alter the returned documents—adding, renaming, nesting and even computing new field values—with an expression that describes the document to return. For example, alter the names of the fields with the following expression to return only two documents.

mysql-py> db.countryinfo.find().\
fields(mysqlx.expr('{"Name": upper(Name), "GNPPerCapita": GNP*1000000/demographics.Population}')).\
limit(2)
[
    {
        "GNPPerCapita": 8038.834951456311,
        "Name": "ARUBA"
    },
    {
        "GNPPerCapita": 263.0281690140845,
        "Name": "AFGHANISTAN"
    }
]
2 documents in set (0.00 sec)

You can apply the limit(), sort(), and skip() methods to manage the number and order of documents returned by the find() method.

To specify the number of documents included in a result set, append the limit() method with a value to the find() method. The following query returns the first five documents in the countryinfo collection.

mysql-py> db.countryinfo.find().limit(5)
... [output removed]
5 documents in set (0.00 sec)

To specify an order for the results, append the sort() method to the find() method. Pass to the sort() method a list of one or more fields to sort by and, optionally, the descending (desc) or ascending (asc) attribute as appropriate. Ascending order is the default order type.

For example, the following query sorts all documents by the IndepYear field and then returns the first eight documents in descending order.

mysql-py> db.countryinfo.find().sort(["IndepYear desc"]).limit(8)
... [output removed]
8 documents in set (0.00 sec)

By default, the limit() method starts from the first document in the collection. You can use the skip() method to change the starting document. For example, to ignore the first document and return the next eight documents matching the condition, pass to the skip() method a value of 1.

mysql-py> db.countryinfo.find().sort(["IndepYear desc"]).limit(8).skip(1)
... [output removed]
8 documents in set (0.00 sec)